Editing Metre Convention

{{Short description|1875 international standardization treaty}}
{{Use Oxford spelling|date=October 2019}}
{{Use dmy dates|date=August 2024}}

[[File:Metre Convention Signatories.svg|thumb|350px|
{|
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| colspan="2" | Metre Convention signatories 
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| {{legend|#008000|Member states}}|| {{legend|#00d000|Associate states}}
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| {{legend|#ff0000|Former member states}}|| {{legend|#ff9e9e|Former associate states}}
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The '''Metre Convention''' ({{langx|fr|link=no|Convention du Mètre}}), also known as the '''Treaty of the Metre''',<ref>
{{cite encyclopedia
|url = http://www.britannica.com/EBchecked/topic/378767/Treaty-of-the-Metre
|title = Treaty of the Metre
|encyclopedia = [[Encyclopædia Britannica]]
|access-date = 28 March 2013
|year = 2013
|archive-date = 11 May 2013
|archive-url = https://web.archive.org/web/20130511003219/http://www.britannica.com/EBchecked/topic/378767/Treaty-of-the-Metre
|url-status = live
}}</ref> is an [[international treaty]] that was signed in Paris on 20 May 1875 by representatives of 17 nations: [[Argentina]], [[Austria-Hungary]], [[Belgium]], [[Brazil]], [[Denmark]], [[France]], [[German Empire|Germany]], [[Kingdom of Italy|Italy]], [[Peru]], [[Portugal]], [[Russian Empire|Russia]], [[Kingdom of Spain (1810-1873)|Spain]], [[Union between Sweden and Norway|Sweden and Norway]], [[Switzerland]], [[Ottoman Empire]], [[United States|United States of America]], and [[Venezuela]].

The treaty created the [[International Bureau of Weights and Measures]] (BIPM), an [[intergovernmental organization]], under the authority of the [[General Conference on Weights and Measures]] (CGPM) and the supervision of the International Committee for Weights and Measures (CIPM). These organizations coordinate international [[metrology]] and the development of internationally recognized [[System of measurement|systems of measurement]].

The Metre Convention established a permanent organizational structure for member governments to act in common accord on all matters relating to units of measurement. The governing organs of the BIPM are:
* The General Conference on Weights and Measures ({{lang|FR|Conférence générale des poids et mesures}} or CGPM)—the plenary organ of the BIPM which consists of the delegates of all the contracting governments, and 
* The International Committee for Weights and Measures ({{lang|FR|Comité international des poids et mesures}} or CIPM)—the direction and supervision organ composed of 18 prominent metrologists from 18 different member states
The headquarters or secretariat of the BIPM is at [[Saint-Cloud]], France. It employs around 70 people and hosts BIPM's formal meetings.

Initially the scope of the Metre Convention covered only units of mass and length. In 1921, at the sixth meeting of the CGPM, convention was amended to its scope to other fields in physics. In 1960, at the eleventh meeting of the CGPM, its system of units was named the [[International System of Units]] ({{lang|fr|Système international d'unités}}, abbreviated SI).<ref>{{Cite web|url=https://www.bipm.org/en/measurement-units/history-si/|title=BIPM – history|website=bipm.org|access-date=27 April 2018|archive-date=7 October 2014|archive-url=https://web.archive.org/web/20141007190842/https://www.bipm.org/en/measurement-units/history-si/|url-status=live}}</ref>

The Metre Convention provides that only nations can be members of the BIPM. In 1999, the CGPM created in the status of associate, to allow non-member states and economic entities to participate in some activities of the BIPM through their national metrology institutes (NMIs).

{{As of|2024|10|16}}, the CGPM had 64 members and 37 associates.

Membership in the CGPM requires payment of substantial fees. Being in arrears with these payments over a span of years has led to expulsion of some former members.

== Background ==
[[File:Systeme-Metrique.jpg|thumb|250px|Woodcut dated 1800 illustrating the new decimal units which became the legal norm across all France on 4 November 1800]]
Before the [[French Revolution]], which started in 1789, [[Units of measurement in France|French units of measurement]] were based on the [[Carolingian Renaissance|Carolingian]] system, introduced by the first [[Holy Roman Emperor]] [[Charlemagne]] (800–814 AD) which in turn were based on ancient Roman measures. Charlemagne brought a consistent system of measures across the entire empire. However, after his death, the empire fragmented and many rulers introduced their own variants of the units of measure.

Some of Charlemagne's units of measure, such as the {{lang|fr|pied du Roi}} (the king's [[Foot (unit)|foot]]) remained virtually unchanged for about a thousand years, while others, such as the {{lang|fr|aune}} ([[ell]] – used to measure cloth) and the {{lang|fr|livre}} ([[Pound (mass)|pound]]) varied dramatically from locality to locality. By the time of the revolution, the number of units of measure had grown to the extent that it was almost impossible to keep track of them.

In England in 1215, clause 35 of [[Magna Carta]] required that the same standards of measurement be applied throughout the realm. The wording of the clause emphasized that "There is to be a single measure ... throughout our realm".<ref>
{{cite web
 |url = https://www.archives.gov/exhibits/featured-documents/magna-carta/translation.html
 |title = Magna Carta
 |date = 6 October 2015
 |translator-first = Nicholas
 |translator-last = Vincent
 |access-date = 30 September 2012
 |archive-date = 15 November 2015
 |archive-url = https://web.archive.org/web/20151115024814/http://www.archives.gov/exhibits/featured-documents/magna-carta/translation.html
 |url-status = live
}}</ref> Five centuries later, when in 1707 [[Acts of Union 1707|England and Scotland were united]] into a single kingdom, the Scots agreed to use the same units of measure that were already established in England.<ref>[[s:Act of Union 1707|Act of Union 1707]], Article 3</ref> During the eighteenth century, in order to facilitate trade, [[Peter the Great]], Czar of Russia adopted the English system of measure.<ref>
{{cite book
 |first1 = Thomas
 |last1 = McGreevy
 |title = The Basis of Measurement: Volume 1 – Historical Aspects
 |page = 166
 |isbn = 0-948251-82-4
 |year = 1995
 |publisher = Pitcon Publishing (Chippenham) Ltd
}}</ref>

From 1668 to 1776 the French standard of length was the [[Toise]] of Châtelet which was fixed outside the [[Grand Châtelet]] in Paris. In 1735 two geodetic standards were calibrated against the Toise of Châtelet. One of them, the Toise of Peru was used for the [[French Geodesic Mission to the Equator]]. In 1766 the Toise of Peru became the official standard of length in France and was renamed Toise of the [[French Academy of Sciences|Academy]] ({{langx|fr|links=no|Toise de l'Académie}}).<ref>{{Cite web |title=What is the unit called a toise? |url=https://www.sizes.com/units/toise.htm |access-date=2025-04-10 |website=www.sizes.com}}</ref><ref>{{Cite web |title=Pied de roi - 1774 - La Toise de l'Académie des Sciences et le Mètre - Musée des arts et métiers - Paris - France |url=https://www.aly-abbara.com/utilitaires/convertisseur/Images/pied-roi-1774-France.html |access-date=2025-04-10 |website=www.aly-abbara.com}}</ref>

Profusion of units of measures was a practical problem of importance before the French Revolution and its reform was one of the items on the agenda of [[National Assembly (French Revolution)|National Assembly]].<ref name=":1">{{Cite news|url=https://www.entreprises.gouv.fr/metrologie/histoire-metre|title=Histoire du mètre|work=Direction Générale des Entreprises (DGE)|access-date=27 December 2017|archive-date=3 October 2015|archive-url=https://web.archive.org/web/20151003055350/http://www.entreprises.gouv.fr/metrologie/histoire-metre|url-status=live}}</ref> In 1799, after the remeasurement of the [[Paris meridian]] arc ({{langx|fr|links=no|Méridienne de France}}) between [[Dunkirk]] and [[Barcelona]] by [[Jean Baptiste Joseph Delambre|Delambre]] and [[Pierre Méchain|Mechain]], the metre was defined as a quarter of a 10-millionth of the Earth circumference or 3 {{lang|fr|[[pied]]s}} (French feet) and 11.296 {{lang|fr|[[ligne]]s}} (lines) of the Toise of the Academy.<ref name=":1" /> [[Charles Maurice de Talleyrand-Périgord|Talleyrand]], an influential leader of the Assembly invited British and American participation in the establishment of a new system, but in the event, the Assembly went it alone and introduced the metre and the [[kilogram]] which were to form the basis of the metric system, manufacturing prototypes which, in 1799, were lodged with Archives.<ref name="McGreevy1">
{{cite book |last1=McGreevy |first1=Thomas |title=The Basis of Measurement: Volume 1 – Historical Aspects |publisher=Pitcon Publishing (Chippenham) Ltd |year=1995 |isbn=0-948251-82-4 |pages=145, 151}}</ref>

Between 1840 and 1870, a number of countries definitively adopted the metric system as their system of measure including France, Spain, many South American republics and many of the Italian and German states (the Netherlands had adopted the system in 1817).<ref name=":1" />

In 1863, the [[International Postal Union]] used grams to express permitted weights of letters. In the 1860s, inspections of the prototype metre revealed wear and tear at the measuring faces of the bar and also that the bar was wont to flex slightly when in use.<ref name="McGreevy1" />

== Cartography and the metre ==
The [[American Revolution]], in which the [[United States]] was supported by [[France]] and [[Spain]],<ref>{{Cite web |last=Ferreiro |first=Larrie D. |date=December 2024 |title=The Rise and Fall and Rise of Spain in the Historiography of the American Revolution |url=https://institutofranklin.net/sites/default/files/revistas/%5B2024-12/The%20Rise%20and%20Fall%20and%20Rise%20of%20Spain%20in%20the%20Historiography%20of%20the%20American%20Revolution_Larrie%20D.%20Ferreiro.pdf |website=Instituto Franklin-UAH}}</ref> led to the founding of the [[United States Coast and Geodetic Survey|Survey of the Coast]] in 1807 and the creation of the [[National Institute of Standards and Technology|Office of Standard Weights and Measures]] in 1830.<ref name="Cajori-1921" /> During the mid-19th century, the metre was adopted in [[Khedivate of Egypt]] an autonomous tributary state of the [[Ottoman Empire]] for [[cadastral surveying]].<ref name="Jamʻīyah al-Jughrāfīyah al-Miṣrīyah-1876">{{Cite book |last=Jamʻīyah al-Jughrāfīyah al-Miṣrīyah |url=http://archive.org/details/bulletindelasoc00almgoog |title=Bulletin de la Société de géographie d'Égypte |date=1876 |publisher=[Le Caire] |others=University of Michigan |pages=5–16}}</ref><ref>{{Cite book |author=Ismāʿīl-Afandī Muṣṭafá |url=https://gallica.bnf.fr/ark:/12148/bpt6k840511v |title=Notes biographiques de S.E. Mahmoud Pacha el Falaki (l'astronome), par Ismail-Bey Moustapha et le colonel Moktar-Bey |date=1886 |pages=10–11 |language=EN}}</ref><ref name="Ismāʿīl-Afandī Muṣṭafá-1864">{{Cite book |author=Ismāʿīl-Afandī Muṣṭafá |url=https://gallica.bnf.fr/ark:/12148/bpt6k62478474 |title=Recherche des coefficients de dilatation et étalonnage de l'appareil à mesurer les bases géodésiques appartenant au gouvernement égyptien / par Ismaïl-Effendi-Moustapha, ... |date=1864 |language=EN}}</ref> In [[continental Europe]], adoption of the [[metric system]] and a better [[standardisation]] of units of measurement marked the [[Second Industrial Revolution|Technological Revolution]], a period in which [[German Empire]] would challenge [[United Kingdom]] as the foremost industrial nation in Europe. This was accompanied by development in [[cartography]] which was a prerequisite for both military operations and the creation of the infrastructures needed for industrial development such as [[Rail transport|railways]]. During the process of [[unification of Germany]], [[Geodesy|geodesists]] called for the establishment of an [[International Bureau of Weights and Measures]] in [[Europe]].<ref name="Alder-2015">{{Cite book |last1=Alder |first1=Ken |title=Mesurer le monde: l'incroyable histoire de l'invention du mètre |last2=Devillers-Argouarc'h |first2=Martine |date=2015 |publisher=Flammarion |isbn=978-2-08-130761-2 |series=Libres Champs |location=Paris |pages=499–520, 517-518}}</ref><ref name="BEG-1868">{{Cite book |url=http://gfzpublic.gfz-potsdam.de/pubman/item/escidoc:108187:4/component/escidoc:272449/Generalbericht.mitteleurop%C3%A4ische.Gradmessung%201867.pdf |title=Bericht über die Verhandlungen der vom 30. September bis 7. October 1867 zu BERLIN abgehaltenen allgemeinen Conferenz der Europäischen Gradmessung |publisher=Central-Bureau der Europäischen Gradmessung |year=1868 |location=Berlin |pages=123–134 |language=german}}</ref>

=== Swiss, American, Spanish and Egyptian cartography ===
[[File:HasslerCollection 001.jpg|thumb|Triangulation near [[New York City]], 1817|left]]

The [[Helvetic Republic]] adopted the [[metric system]] by law in 1801.<ref>{{Cite web |title=Système métrique |url=https://hls-dhs-dss.ch/fr/articles/013754/2014-05-22/ |access-date=2025-04-08 |website=hls-dhs-dss.ch |language=fr}}</ref> In 1805, a Swiss immigrant [[Ferdinand Rudolph Hassler]] brought copies of the French metre and kilogram to the United States. In 1830 the [[United States Congress|Congress]] decided to create uniform standards for length and weight in the United States.<ref name=":3">{{Cite web |title=e-expo: Ferdinand Rudolf Hassler |url=https://www.f-r-hassler.ch/en/weights/index.html |access-date=2025-04-07 |website=www.f-r-hassler.ch}}</ref> Hassler was mandated to work out the new standards and proposed to adopt the metric system. The United States Congress opted for the [[Yard#Physical standards|British Parliamentary Standard Yard of 1758]] and the British [[Imperial units#Mass and weight|Troy Pound of 1824]] as length and weight standards.<ref name=":3" /> Nevertheless Ferdinand Rudolph Hassler's use of the metre and the creation of the [[National Institute of Standards and Technology|Office of Standard Weights and Measures]] as an office within the [[United States Coast and Geodetic Survey|Coast Survey]] contributed to the introduction of the [[Metric Act of 1866]] allowing the use of the metre in the United States.<ref name="Metric Act of 1866">{{Cite web |title=Metric Act of 1866 – US Metric Association |url=https://usma.org/laws-and-bills/metric-act-of-1866#locale-notification |access-date=2021-03-15 |website=usma.org}}</ref>

In 1816, Ferdinand Rudolph Hassler was appointed first Superintendent of the [[United States Coast and Geodetic Survey|Survey of the Coast]].<ref>{{cite web |url=https://celebrating200years.noaa.gov/historymakers/hassler/welcome.html |title=NOAA 200th Top Tens: History Makers: Ferdinand Rudolph Hassler |publisher=National Oceanic and Atmospheric Administration |location=US |date=2024-03-19 |access-date=2024-10-17}}</ref><ref name="Cajori-1921">{{Cite journal |last=Cajori |first=Florian |date=1921 |title=Swiss Geodesy and the United States Coast Survey |url=https://www.jstor.org/stable/6721 |journal=The Scientific Monthly |volume=13 |issue=2 |pages=117–129 |bibcode=1921SciMo..13..117C |issn=0096-3771}}</ref> Trained in geodesy in Switzerland, France and [[Germany]], Hassler had brought a standard metre made in Paris to the United States in October 1805. He designed a baseline apparatus which instead of bringing different bars in actual contact during measurements,<ref name="Cajori-1921" /> used only one bar calibrated on the Committee meter, an authenthic copy of the {{Lang|fr|Mètre des Archives}},<ref>{{Cite book |url=https://play.google.com/store/books/details?id=NiEEAQAAIAAJ |title=National Bureau of Standards Miscellaneous Publication |date=1966 |publisher=U.S. Government Printing Office |pages=529 |language=en}}</ref><ref name=":10">{{Cite journal |last=Clarke |first=Alexander Ross |last2=James |first2=Henry |date=1873 |title=XIII. Results of the comparisons of the standards of length of England, Austria, Spain, United States, Cape of Good Hope, and of a second Russian standard, made at the Ordnance Survey Office, Southampton. With a preface and notes on the Greek and Egyptian measures of length by Sir Henry James |url=https://royalsocietypublishing.org/doi/10.1098/rstl.1873.0014 |journal=Philosophical Transactions of the Royal Society of London |volume=163 |pages=445–469 |doi=10.1098/rstl.1873.0014}}</ref> and optical contact.<ref name="Cajori-1921" /><ref>{{Cite book |last1=American Philosophical Society. |url=https://www.biodiversitylibrary.org/item/26092 |title=Transactions of the American Philosophical Society |last2=Society |first2=American Philosophical |last3=Poupard |first3=James |date=1825 |volume=new ser.:v.2 (1825) |location=Philadelphia [etc.] |pages=234–278}}</ref> In 1830, Hassler became head of the Office of Weights and Measures, which became a part of the Survey of the Coast. He compared various units of length used in the [[United States]] at that time and measured [[Thermal expansion|coefficients of expansion]] to assess temperature effects on the measurements.<ref name="Parr-2006">{{Cite journal |last=Parr |first=Albert C. |date=2006-04-01 |title=A Tale About the First Weights and Measures Intercomparison in the United States in 1832 |url=https://www.nist.gov/publications/tale-about-first-weights-and-measures-intercomparison-united-states-1832 |journal=Journal of Research of the National Institute of Standards and Technology |language=en |volume=111 |issue=1 |pages=31–32, 36 |doi=10.6028/jres.111.003 |pmc=4654608 |pmid=27274915 |via=NIST}}</ref> In 1834, Hassler, measured at [[Fire Island]] the first [[Baseline (surveying)|baseline]] of the Survey of the Coast,<ref name=":5">{{Cite book |last1=Hassler |first1=Harriet |url=http://archive.org/details/ferdinandrudolph1068hass |title=Ferdinand Rudolph Hassler (1770–1843) |last2=Burroughs |first2=Charles A. |date=2007 |others=NIST Research Library |pages=51–52}}</ref> shortly before [[Louis Puissant]] declared to the French Academy of Sciences in 1836 that Jean Baptiste Joseph Delambre and Pierre Méchain had made errors in the [[Arc measurement|meridian arc measurement]], which had been used to determine the length of the metre.<ref name="Lebon-1899">{{Cite book |last=Lebon |first=Ernest |url=https://gallica.bnf.fr/ark:/12148/bpt6k949666 |title=Histoire abrégée de l'astronomie / par Ernest Lebon,... |date=1899 |pages=168–171 |language=EN}}</ref><ref>{{Cite book |last=Puissant |first=Louis |url=https://gallica.bnf.fr/ark:/12148/bpt6k5323385b |title=Nouvelle détermination de la distance méridienne de Montjouy à Formentera, dévoilant l'inexactitude de celle dont il est fait mention dans la base du système métrique décimal, par M. Puissant,... lu à l'Académie des sciences, le 2 mai 1836 |language=EN}}</ref>[[File:Appareil_Ibáñez.jpg|thumb|313x313px|Ibáñez apparatus calibrated on the metric Spanish standard and used at [[Aarberg]], in [[canton of Bern]], [[Switzerland]] in 1880.<ref>{{Cite book |last1=Hirsch |first1=A. |title=Le Réseau de Triangulation suisse |last2=Dumur |first2=J. |publisher=Commission géodésique suisse |year=1888 |volume=Troisième volume. La Mensuration des Bases |pages=3–4 |language=fr}}</ref>]]
In 1855, the Dufour map (French: ''Carte Dufour''), the first [[Topographic Map of Switzerland|topographic map of Switzerland]] for which the metre was adopted as the unit of length, won the gold medal at the Exposition Universelle.<ref>{{Cite news |last=Abplanalp |first=Andrej |date=2019-07-14 |title=Henri Dufour et la carte de la Suisse |url=https://blog.nationalmuseum.ch/fr/2019/07/dufour-le-cartographe/ |archive-url=https://web.archive.org/web/20241225163218/https://blog.nationalmuseum.ch/fr/2019/07/dufour-le-cartographe/ |archive-date=25 December 2024 |access-date=2025-01-25 |work=Musée national - Blog sur l'histoire suisse |language=de-DE |url-status=live }}</ref><ref>{{Cite journal |last=Dufour |first=G.-H. |date=1861 |title=Notice sur la carte de la Suisse dressée par l'État Major Fédéral |url=https://www.persee.fr/doc/globe_0398-3412_1861_num_2_1_7582 |journal=Le Globe. Revue genevoise de géographie |volume=2 |issue=1 |pages=5–22 |doi=10.3406/globe.1861.7582}}</ref> However, the baselines for this map were measured in 1834 with three toises long measuring rods calibrated on a toise made in 1821 by [[Jean Nicolas Fortin]] for [[Friedrich Georg Wilhelm von Struve]].<ref>{{Cite journal |last=Seligmann |first=A. E. M. |date=1923 |title=La Toise de Belgique |journal=Ciel et Terre, Bulletin of the Société Belge d'Astronomie |volume=39 |page=25}}</ref><ref name="Clarke-1867">{{Cite journal |last1=Clarke |first1=Alexander Ross |last2=James |first2=Henry |date=1867-01-01 |title=X. Abstract of the results of the comparisons of the standards of length of England, France, Belgium, Prussia, Russia, India, Australia, made at the ordnance Survey Office, Southampton |url=https://royalsocietypublishing.org/doi/10.1098/rstl.1867.0010 |journal=Philosophical Transactions of the Royal Society of London |volume=157 |page=174 |doi=10.1098/rstl.1867.0010 |s2cid=109333769}}</ref> The Spanish standard, a geodetic measuring device calibrated on the metre devised by [[Carlos Ibáñez e Ibáñez de Ibero]] and [[Frutos Saavedra Meneses]], was also displayed by [[Jean Brunner]] at the Exhibition.<ref>{{Cite periodical |last=Brenni |first=Paolo |date=1996 |title=19th Century French Scientific Instrument Makers XI: The Brunners and Paul Gauher |url=https://www.unav.es/gep/TheBrunnersCartaParis.pdf |archive-url=https://web.archive.org/web/20241203014633/https://www.unav.es/gep/TheBrunnersCartaParis.pdf |archive-date=3 December 2024 |access-date=2025-01-25 |periodical=Bulletin of the Scientific Instrument Society |number=49 |url-status=live }}</ref><ref>{{Cite journal |last=Brenni |first=Paolo |date=1996 |title=19th Century French Scientific Intrument Makers |url=https://www.unav.es/gep/TheBrunnersCartaParis.pdf |journal=Bulletin of the Scientific Instrument Society |issue=49 |page=4 |archive-url=https://web.archive.org/web/20241203014633/https://www.unav.es/gep/TheBrunnersCartaParis.pdf |archive-date=3 December 2024}}</ref> Carlos Ibáñez e Ibáñez de Ibero recognized that the end standards with which the most perfect devices of the eighteenth century and those of the first half of the nineteenth century were still equipped, that [[Jean-Charles de Borda]] or [[Friedrich Bessel|Friedrich Wilhelm Bessel]] simply joined measuring the intervals by means of screw tabs or glass wedges, would be replaced advantageously for accuracy by microscopic measurements, a system designed in [[Switzerland]] by Ferdinand Rudolph Hassler and [[Johann Georg Tralles]],<ref>{{Cite web |last=Wolf |first=Rudolf |date=1891-01-01 |title=Histoire de l'appareil Ibañez-Brunner in Comptes rendus hebdomadaires des séances de l'Académie des sciences / publiés... par MM. les secrétaires perpétuels |url=https://gallica.bnf.fr/ark:/12148/bpt6k3068q |access-date=2023-08-31 |website=Gallica |pages=370–371 |language=FR}}</ref> and which Ibáñez ameliorated using a single standard with lines marked on the bar. Regarding the two methods by which the effect of temperature was taken into account, Ibáñez used both the bimetallic rulers, in platinum and brass, which he first employed for the central base of Spain,<ref name="Brunner-18572">{{Cite web |last=Brunner |first=Jean |date=1857-01-01 |title=Appareil construit pour les opérations au moyen desquelles on prolongera dans toute l'étendue de l'Espagne le réseau trigonométrique qui couvre la France in Comptes rendus hebdomadaires des séances de l'Académie des sciences / publiés... par MM. les secrétaires perpétuels |url=https://gallica.bnf.fr/ark:/12148/bpt6k3001w |access-date=2023-08-31 |website=Gallica |pages=150–153 |language=FR}}</ref> and the simple iron ruler with inlaid mercury thermometers which was used in Switzerland.<ref name=":6" /><ref name=":11">{{Cite EB1911 |wstitle= Geodesy |volume = 11 |last1= Clarke |first1= Alexander Ross |author-link1= Alexander Ross Clarke |last2= Helmert |first2= Friedrich Robert |author-link2= Friedrich Robert Helmert |pages= 607-615 |short=1}}</ref> On the sidelines of the [[Exposition Universelle (1855)]] and the second [[International Statistical Institute|Congress of Statistics]] held in Paris, an association with a view to obtaining a uniform decimal system of measures, weights and currencies was created in 1855.<ref name=":4" /> Under the impetus of this association, a Committee for Weights and Measures and Monies (French: ''Comité des poids, mesures et monnaies'') would be created during the [[Exposition Universelle (1867)]] in Paris and would call for the international adoption of the metric system.<ref name=":8">{{Cite web |title=History – The BIPM 150 |url=https://thebipm150.org/history/ |access-date=2025-04-08 |language=fr-FR}}</ref><ref name=":4" />

[[Egyptian astronomy]] has ancient roots which were revived in the 19th century by the modernist impetus of [[Muhammad Ali of Egypt|Muhammad Ali]] who founded in Sabtieh, [[Boulaq]] district, in [[Cairo]] an Observatory which he was keen to keep in harmony with the progress of this science still in progress.<ref name="Ismāʿīl-Afandī Muṣṭafá-1864" /><ref name="Jamʻīyah al-Jughrāfīyah al-Miṣrīyah-1876" /> In 1858, a Technical Commission was set up to continue [[cadastral surveying]] inaugurated under Muhammad Ali. This Commission suggested to Viceroy [[Sa'id of Egypt|Mohammed Sa'id Pasha]] to buy geodetic devices which were ordered in France. While [[Mahmud Ahmad Hamdi al-Falaki]] was in charge, in Egypt, of the direction of the work of the general map, the viceroy entrusted to [[Ismail Mustafa al-Falaki]] the study, in Europe, of the precision apparatus calibrated against the metre intended to measure the geodesic bases and already built by [[Jean Brunner]] in Paris. Ismail Mustafa had the task to carry out the experiments necessary for determining the expansion coefficients of the two platinum and brass bars, and to compare the Egyptian standard with a known standard. The Spanish standard designed by Carlos Ibáñez e Ibáñez de Ibero and Frutos Saavedra Meneses was chosen for this purpose, as it had served as a model for the construction of the Egyptian standard.<ref name="Jamʻīyah al-Jughrāfīyah al-Miṣrīyah-1876" /><ref name="Ismāʿīl-Afandī Muṣṭafá-1864" /> In addition, the Spanish standard had been compared with [[Jean-Charles de Borda|Borda]]'s double-toise N°&nbsp;1, which served as a comparison module for the measurement of all geodesic bases in France,<ref name="Soler-1997">{{Cite journal |last=Soler |first=T. |date=1997-02-01 |title=A profile of General Carlos Ibáñez e Ibáñez de Ibero: first president of the International Geodetic Association |journal=Journal of Geodesy |language=en |volume=71 |issue=3 |pages=176–188 |bibcode=1997JGeod..71..176S |citeseerx=10.1.1.492.3967 |doi=10.1007/s001900050086 |issn=1432-1394 |s2cid=119447198}}</ref><ref name="Brunner">{{Cite web |last=Brunner |first=Jean |date=1857 |title=Comptes rendus hebdomadaires des séances de l'Académie des sciences / publiés... par MM. les secrétaires perpétuels |url=https://gallica.bnf.fr/ark:/12148/bpt6k3001w |access-date=2019-05-15 |website=Gallica |pages=150–153 |language=FR}}</ref> and was also to be compared to the Ibáñez apparatus.<ref name=":10" /><ref name="Soler-1997" /> In 1954, the connection of the southerly extension of the [[Struve Geodetic Arc]] with an arc running northwards from [[South Africa]] through [[Egypt]] would bring the course of a major [[meridian arc]] back to land where [[Eratosthenes]] had founded [[geodesy]].<ref>{{Cite news |title=Nomination of the STRUVE GEODETIC ARC for inscription on the WORLD HERITAGE LIST |url=https://whc.unesco.org/uploads/nominations/1187.pdf |pages=40, 143–144}}</ref>

=== European geodesy ===
In Europe, except Spain,<ref name="Brunner-18572" /> surveyors continued to use measuring instruments calibrated on the Toise of Peru.<ref name="Quinn-2012">{{Cite book |last=Quinn |first=T. J. |title=From artefacts to atoms: the BIPM and the search for ultimate measurement standards |date=2012 |publisher=Oxford University Press |isbn=978-0-19-990991-9 |location=Oxford |pages=9, 11, 20, 37–38, 91–92, 70–72, 114–117, 144–147, 8 |oclc=861693071}}</ref> Among these, the toise of Bessel and the apparatus of Borda were respectively the main references for geodesy in [[Prussia]] and in [[France]]. These measuring devices consisted of bimetallic rulers in platinum and brass or iron and zinc fixed together at one extremity to assess the variations in length produced by any change in temperature. The combination of two bars made of two different metals allowed to take [[thermal expansion]] into account without measuring the temperature.<ref>{{Cite web |title=Borda et le système métrique |url=https://mesurelab.fr/wp/metrologie/histoire-de-la-metrologie/borda-et-le-systeme-metrique/ |archive-url=https://web.archive.org/web/20230829055653/https://mesurelab.fr/wp/metrologie/histoire-de-la-metrologie/borda-et-le-systeme-metrique/ |archive-date=29 August 2023 |access-date=2023-08-29 |website=Association Mesure Lab |language=fr-FR}}</ref><ref name="Viik-2006">{{Cite news |last=Viik |first=T |date=2006 |title=F. W. Bessel and geodesy |work=Struve Geodetic Arc, 2006 International Conference, The Struve Arc and Extensions in Space and Time, Haparanda and Pajala, Sweden, 13–15 August 2006 |pages=10, 6 |citeseerx=10.1.1.517.9501}}</ref> A French scientific instrument maker, [[Jean Nicolas Fortin]], made three direct copies of the Toise of Peru, one for [[Friedrich Georg Wilhelm von Struve]], a second for [[Heinrich Christian Schumacher]] in 1821 and a third for Friedrich Wilhelm Bessel in 1823. In 1831, [[Henri-Prudence Gambey]] also realised a copy of the Toise of Peru which was kept at [[Altona Observatory]].<ref>{{Cite book |last=Wolf |first=M. C |title=Recherches historiques sur les étalons de poids et mesures de l'observatoire et les appareils qui ont servi a les construire. |date=1882 |publisher=Gauthier-Villars |location=Paris |pages=7–8, 20, 32 |language=French |oclc=16069502}}</ref><ref>{{Cite book |last=Baeyer |first=Johann Jacob |title=Grösse und Figur der Erde |publisher=Georg Reimer |year=1861 |location=Berlin |publication-date=1861 |pages=87–94 |language=de}}</ref>

In the second half of the 19th century, the creation of the [[International Association of Geodesy|Central European Arc Measurement]] ({{Langx|de|Mitteleuropäische Gradmessung}}) would mark, following [[Carl Friedrich Gauss]],<ref>{{Cite book |last=Tardi |first=Pierre (1897-1972) Auteur du texte |url=https://gallica.bnf.fr/ark:/12148/bpt6k3355272d/f74.item |title=Traité de géodésie / par le capitaine P. Tardi ; préface par le général G. Perrier |date=1934 |pages=34 |language=EN}}</ref><ref name="Quinn-20122" /> Friedrich Wilhelm Bessel and Friedrich Georg Wilhelm von Struve examples,<ref name=":9">{{Cite EB1911|wstitle=Earth, Figure of the|volume=8|last1=Clarke|first1=Alexander Ross|author-link1=Alexander Ross Clarke|last2=Helmert|first2=Friedrich Robert|author-link2=Friedrich Robert Helmert|pages=801-813|short=1}}</ref> the systematic adoption of more rigorous methods among them the application of the [[least squares]] in geodesy.<ref>{{Cite web |title=Mesure du 1er mètre: une erreur qui changea le monde |url=https://www.techniques-ingenieur.fr/actualite/articles/mesure-du-1er-metre-une-erreur-qui-changea-le-monde-2715/ |access-date=December 30, 2020 |website=Techniques de l'Ingénieur |language=fr-FR}}</ref><ref name="Lebon-1899" /> It became possible to accurately measure parallel arcs, since the difference in longitude between their ends could be determined thanks to the invention of the [[electrical telegraph]].<ref name="Clarke-1867" /> Furthermore, advances in [[metrology]] combined with those of [[gravimetry]] have led to a new era of [[geodesy]]. If precision metrology had needed the help of geodesy, the latter could not continue to prosper without the help of metrology. It was then necessary to define a single unit to express all the measurements of terrestrial arcs and all determinations of the [[gravitational acceleration]] by means of pendulum.<ref>Carlos Ibáñez e Ibáñez de Ibero, ''Discursos leidos ante la Real Academia de Ciencias Exactas Fisicas y Naturales en la recepcion pública de Don Joaquin Barraquer y Rovira'', Madrid, Imprenta de la Viuda e Hijo de D.E. Aguado, 1881, p. 78</ref>

In 1866, an important concern was that the Toise of Peru, the standard of the toise constructed in 1735 for the [[French Geodesic Mission to the Equator]], might be so much damaged that comparison with it would be worthless,<ref name="Clarke-1867" /> while Bessel had questioned the accuracy of copies of this standard belonging to [[Altona Observatory|Altona]] and [[Koenigsberg Observatory|Koenigsberg]] Observatories, which he had compared to each other about 1840.<ref>{{Cite journal |last=Bessel |first=Friedrich Wilhelm |date=1840-04-01 |title=Über das preufs. Längenmaaß und die zu seiner Verbreitung durch Copien ergriffenen Maaßregeln. |url=https://ui.adsabs.harvard.edu/abs/1840AN.....17..193B |journal=Astronomische Nachrichten |volume=17 |issue=13 |page=193 |bibcode=1840AN.....17..193B |doi=10.1002/asna.18400171302 |issn=0004-6337}}</ref> In fact, the length of Bessel's Toise, which according to the then legal ratio between the metre and the Toise of Peru, should be equal to 1.9490348 m, would be found to be 26.2·10<sup>-6</sup> m greater during measurements carried out by [[Justin-Mirande René Benoit|Jean-René Benoît]] at the International Bureau of Weights and Measures. It was the consideration of the divergences between the different toises used by geodesists that led the [[International Association of Geodesy|European Arc Measurement]] ({{langx|de|links=no|Europäische Gradmessung}} ) to consider, at the meeting of its Permanent Commission in Neuchâtel in 1866, the founding of a World Institute for the Comparison of Geodetic Standards, the first step towards the creation of the International Bureau of Weights and Measures.<ref>Guillaume, Charles-Édouard (1927). ''La Création du Bureau International des Poids et Mesures et son Œuvre'' [''The creation of the International Bureau of Weights and Measures and its work'']. Paris: Gauthier-Villars. p. 129-130.</ref><ref name="Pérard-1957" /> [[Spain]] joined the [[International Association of Geodesy|European Arc Measurement]] at this meeting.<ref>{{Cite web |date=2013-06-22 |title=El General Ibáñez e Ibáñez de Ibero, Marqués de Mulhacén {{!}} Revista e-medida |url=https://www.e-medida.es/numero-4/el-general-ibanez-e-ibanez-de-ibero-marques-de-mulhacen/ |access-date=2025-04-08 |language=es}}</ref> In 1867 at the second General Conference of the European Arc Measurement held in [[Berlin]], the question of international standard of length was discussed in order to combine the measurements made in different countries to determine the size and shape of the Earth.<ref name=":0">{{Cite web |title=A Note on the History of the IAG |url=http://www.iag-aig.org/index.php?tpl=text&id_c=80&id_t=143 |url-status=live |archive-url=https://web.archive.org/web/20170722002232/http://www.iag-aig.org/index.php?tpl=text&id_c=80&id_t=143 |archive-date=22 July 2017 |access-date=16 May 2017 |website=IAG Homepage}}</ref> The conference recommended the adoption of the metric system (replacing [[Friedrich Bessel|Bessel]]'s toise) and the creation of an International Metre Commission.<ref name=":0" />

=== Saint Petersburg Academy ===
[[Ferdinand Rudolph Hassler]]'s metrological and geodetic work also had a favourable response in Russia.<ref name="Parr-2006" /><ref name="Cajori-1921" /> In 1869, the [[Russian Academy of Sciences|Saint Petersburg Academy of Sciences]] sent to the French Academy of Sciences a report drafted by [[Otto Wilhelm von Struve]], who secured, in 1860, the co-operation of Prussia, Belgium, France and England to the measurement of the European arc of parallel in 52° latitude,<ref name=":11" /><ref name="Clarke-1867" /> [[Heinrich von Wild]], the Swiss born director of the Central Geophysical Observatory in [[Saint Petersburg]],<ref>{{Cite web |date=2015-12-08 |title=History of IMO |url=https://public-old.wmo.int/en/about-us/who-we-are/history-IMO |url-status=dead |archive-url=https://web.archive.org/web/20231218170901/https://public-old.wmo.int/en/about-us/who-we-are/history-IMO |archive-date=December 18, 2023 |access-date=2023-10-12 |website=public.wmo.int |language=en}}</ref> and [[Moritz von Jacobi]], whose theorem has long supported the assumption of an ellipsoid with three unequal axes for the figure of the Earth,<ref name=":9" /> inviting his French counterpart to undertake joint action to ensure the universal use of the [[metric system]] in all scientific work.<ref name="Guillaume-1916" /> The [[French Academy of Sciences]] and the [[Bureau des Longitudes]] in Paris drew the attention of the French government to this issue. In November 1869, [[Napoleon III]] issued invitations to join the International Metre Commission in Paris.<ref name=":8" /><ref>{{Cite web |title=BIPM – International Metre Commission |url=https://www.bipm.org/en/measurement-units/history-si/international-metre-commission.html |url-status=dead |archive-url=https://web.archive.org/web/20180109182826/https://www.bipm.org/en/measurement-units/history-si/international-metre-commission.html |archive-date=9 January 2018 |access-date=9 January 2018 |website=bipm.org}}</ref>

=== The International Metre Commission (1870/1872) ===
Prior to the 1870 conference, French politicians had feared that the British might reject the existing metre and would prefer to have new value of its theoretical length. However, [[James Clerk Maxwell]] wrote in 1865 that no scientist could become famous proposing a metre deduced from new measurements of the size of the Earth,<ref>{{Cite book |last=Maxwell |first=James Clerk |url=https://archive.org/details/electricandmagne01maxwrich/page/n39/mode/2up |title=A treatise on electricity and magnetism |date=1873 |publisher=Oxford : Clarendon Press |others=University of California Libraries |pages=3}}</ref> while [[Adolphe Hirsch]] would recall, in his 1891 [[obituary]] of Carlos Ibáñez e Ibáñez de Ibero, that the International Metre Commission had decided not to propose a new length for the metre.<ref name=":6">{{Cite book |last=Hirsch |first=Adolphe |url=https://play.google.com/store/books/details?id=M1PnAAAAMAAJ |title=Comptes-rendus des séances de la Commission permanente de l'Association géodésique internationale réunie à Florence du 8 au 17 octobre 1891 |date=1892 |publisher=De Gruyter, Incorporated |isbn=978-3-11-128691-4 |pages=101-109 |language=fr}}</ref><ref name="Guillaume-1916">{{Cite journal |last=Guillaume |first=Ed. |date=1916-01-01 |title=Le Systeme Metrique est-il en Peril? |url=https://ui.adsabs.harvard.edu/abs/1916LAstr..30..242G |journal=L'Astronomie |volume=30 |pages=244–245 |bibcode=1916LAstr..30..242G |issn=0004-6302}}</ref>

In July 1870, two weeks before the conference was due to start, the [[Franco-Prussian War]] broke out. Although the delegates did meet (without a German delegation), it was agreed that the conference should be recalled once all the delegates (including the German delegation) were present.<ref name="Adler" /> Following the war, which resulted in Napoleon III's exile, Germany and Italy, now unified nations, adopted the metric system as their national system of units, but with the prototype copy of the kilogram and metre under the control of the [[French Third Republic]].<ref name=":7" /> In 1872 the new republican government reissued the invitations and the same year scientists from thirty European and American countries met in Paris.<ref name=":7">
{{cite book
 |title = The Measure of all Things – The Seven-Year-Odyssey that Transformed the World
 |last= Alder
 |first= Ken
 |year= 2002
 |pages = 348–354
 |publisher= Abacus
 |location= London
 |isbn= 0-349-11507-9
}}</ref>

When the International Metre Commission was reconvened in 1872, it was proposed that new prototype metre and kilogram standards be manufactured to reproduce the values of the existing artifacts as closely as possible.<ref name="Adler">{{cite book |last=Alder |first=Ken |title=The Measure of all Things – The Seven-Year-Odyssey that Transformed the World |publisher=Abacus |year=2002 |isbn=0-349-11507-9 |location=London |page=354}}</ref> Indeed, since its origin, the metre had kept a double definition; it was both the ten-millionth part of the quarter meridian and the length represented by the ''Mètre des Archives''. The first was historical, the second was metrological. There was much discussion, considering the opportunity either to keep as definitive the units represented by the metre and kilogram standards of the Archives, or to return to the primitive definitions, and to correct the units to bring them closer to them. The first solution prevailed, in accordance with common sense and in accordance with the advice of the French Academy of Sciences. Abandoning the values represented by the standards, would have consecrated an extremely dangerous principle, that of the change of units to any progress of measurements; the [[Metric system|Metric System]] would be perpetually threatened with change, that is to say with ruin.<ref name="Guillaume-1916" /> The Commission decided the maintenance of new international standards rather than using French existing standards which, at that time, were 70 years old and which, through wear and tear, might not be exactly the same as when they had been adopted in 1799.<ref name="Adler" />  Thus the Commission called for the creation of a new international prototype metre which length would be as close as possible to that of the ''Mètre des Archives'' and the arrangement of a system where national standards could be compared with it.<ref name="Guillaume-1916" />

=== The 1874 metre-alloy ===
[[File:Metre alloy.jpg|thumb|Preparing the first metre-alloy in May 1874, at the Conservatoire des Arts et Métiers, Paris]]
On 6 May 1873 during the 6th session of the French section of the Metre Commission, [[Henri Étienne Sainte-Claire Deville]] cast a 20-kilogram platinum-iridium ingot from Matthey in his laboratory at the [[École normale supérieure (Paris)]]. On 13 May 1874, 250 kilograms of platinum-iridium to be used for several national prototypes of the metre was cast at the [[Conservatoire national des arts et métiers]].<ref name="BIPM-150" /> When a conflict broke out regarding the presence of impurities in the metre-alloy of 1874, a member of the Preparatory Committee since 1870 and president of the Permanent Committee of the International Metre Commission,<ref>{{Cite book |last=Bigourdan |first=Guillaume |url=https://archive.org/details/lesystmemtri00bigo/page/n345/mode/2up |title=Le système métrique des poids et mesures ; son établissement et sa propagation graduelle, avec l'histoire des opérations qui ont servi à déterminer le mètre et le kilogramme |date=1901 |publisher=Paris : Gauthier-Villars |others=University of Ottawa |pages=313}}</ref> [[Carlos Ibáñez e Ibáñez de Ibero]] intervened with the [[French Academy of Sciences]] to rally France to the project to create an International Bureau of Weights and Measures equipped with the scientific means necessary to redefine the units of the [[metric system]] according to the progress of sciences.<ref name="Pérard-19572">{{Cite web |last=Pérard |first=Albert |date=1957 |title=Carlos Ibáñez e Ibáñez de Ibero (14 avril 1825 – 29 janvier 1891), par Albert Pérard (inauguration d'un monument élevé à sa mémoire) |url=https://www.academie-sciences.fr/pdf/eloges/ibanez_notice.pdf |website=Institut de France – Académie des sciences |pages=26–28}}</ref> In fact, the chemical analysis of the alloy produced in 1874 by the French section revealed contamination by [[ruthenium]] and [[iron]] which led the [[General Conference on Weights and Measures|International Committee for Weights and Measures]] to reject, in 1877, the prototypes produced by the French section from the 1874 alloy. It also seemed at the time that the production of prototypes with an X profile was only possible through the [[extrusion]] process, which resulted in iron contamination. However, it soon turned out that the prototypes designed by [[Henri Tresca]] could be produced by [[Milling (machining)|milling]].<ref name="Quinn-20122">{{Cite book |last=Quinn |first=T. J. |title=From artefacts to atoms: the BIPM and the search for ultimate measurement standards |date=2012 |publisher=Oxford University Press |isbn=978-0-19-990991-9 |location=Oxford |pages=3-10, 14, 90-91, 56-57, 72, 108, 56-57 |oclc=861693071}}</ref>

== The 1875 conferences in Paris ==

The principal tasks facing the delegates at the 1875 Diplomatic Conference on the Metre was the replacement of the existing metre and kilogram artefacts that were held by the French Government and the setting up of an organization to administer the maintenance of standards around the globe. The conference did not concern itself with other units of measure. The conference had undertones of Franco-German political manoeuvring, particularly since the French had been humiliated by the Prussians during the war a few years previously. Although France lost control of the metric system, they ensured that it passed to international rather than German control and that the international headquarters were in Paris.<ref name=Adler/>

While the German astronomer [[Wilhelm Julius Foerster]] along with the Russian and Austrian representatives had boycotted the Permanent Committee of the International Metre Commission in order to prompt the reunion of the Diplomatic Conference of the Metre and  to promote the foundation of a permanent International Bureau of Weights and Measures,<ref name="Poids-1903">{{Cite book |last=Comité Interational des Poids et Mesures |title=Procès-Verbaux des Séances. Deuxième Série. Tome II. Session de 1903 |publisher=Gauthier-Villars |location=Paris |pages=5–7}}</ref> Adolphe Hirsch, delegate of Switzerland at this Diplomatic Conference in 1875, conformed to the opinion of [[Italy]] and [[Spain]] to create, in spite of French reluctance, the International Bureau of Weights and Measures in France as a permanent institution at the disadvantage of the ''[[Conservatoire national des arts et métiers]]''.<ref>{{Cite web |date=30 March 1875 |title=Bericht der schweizerischen Delegierten an der internationalen Meterkonferenz an den Bundespräsidenten und Vorsteher des Politischen Departements, J. J. Scherer in Erwin Bucher, Peter Stalder (ed.), Diplomatic Documents of Switzerland, vol. 3, doc. 66, dodis.ch/42045, Bern 1986. |url=https://dodis.ch/42045 |website=Dodis}}</ref>

In 1875, the Permanent Commission of the European Arc Measurement would also hold its reunion in Paris and decide the creation of an international geodetic standard for baselines' measurement calibrated against the metre.<ref>{{Cite web |last=Hirsch |first=Adolphe |title=Bulletin de la Société des Sciences Naturelles de Neuchâtel |url=https://www.e-periodica.ch/digbib/view?pid=bsn-001:1874:10#581 |access-date=2025-04-08 |website=E-Periodica |page=255 |language=de}}</ref> [[Second French Empire|French Empire]] had hesitated for a long time before giving in to the demands of the European Arc Measurement, which asked the French geodesists to take part in its work. It was only after the [[Franco-Prussian War]], that [[Charles-Eugène Delaunay]] represented [[France]] at the Congress of [[Vienna]] in 1871. In 1874, [[Hervé Faye]] was appointed member of the Permanent Commission of the European Arc Measurement presided by Carlos Ibáñez e Ibáñez de Ibero who was collaborating with the French on the extension and  remeasurement of the [[Arc measurement of Delambre and Méchain#Extension of Greenwich meridian arc|meridian arc of Delambre and Méchain]] since 1853.<ref name="Lebon-1899" /><ref name="Soler-1997" />

Spain notably supported France for these outcomes and the first president of the International Committee for Weights and Measures,<ref>{{Cite book |last=Comité international des poids et mesures |first= |url=https://play.google.com/books/reader?id=QgkAAAAAMAAJ&pg=GBS.PA3&hl=fr |title=Procès-verbaux des séances de 1875-1876 |date=1876 |publisher=Bureau international des poids et mesures. |pages=3 |language=fr}}</ref> the Spanish geodesist, Carlos Ibáñez e Ibáñez de Ibero received the [[List of foreign recipients of the Légion d'Honneur|Grand Officer medal of the Légion d'Honneur]] for his diplomatic role on this issue and was awarded the [[Poncelet Prize]] for his scientific contributions to metrology and geodesy.<ref>{{Cite web|url=http://www.academie-sciences.fr/fr/|title=Carlos IBAÑEZ DE IBERO (14 avril 1825 – 29 janvier 1891), par Albert Pérard (inauguration d'un monument élevé à sa mémoire)|last=Pérard|first=Albert|date=1957|website=Institut de France Académie des Sciences|archive-url=https://web.archive.org/web/20170517112721/http://www.academie-sciences.fr/fr/|archive-date=17 May 2017|access-date=18 May 2017|url-status=bot: unknown}}</ref> Indeed, Carlos Ibáñez e Ibáñez de Ibero, first president of the [[International Association of Geodesy|International Geodetic Association]], played a pivotal role in reconciling French and German interests.<ref name="Soler-1997" /><ref name="Pérard-1957">{{Cite web |last=Pérard |first=Albert |date=1957 |title=Carlos Ibáñez e Ibáñez de Ibero (14 avril 1825 – 29 janvier 1891), par Albert Pérard (inauguration d'un monument élevé à sa mémoire) |url=https://www.academie-sciences.fr/pdf/eloges/ibanez_notice.pdf |website=Institut de France – Académie des sciences |pages=26–28}}</ref>

=== Reference standards ===
[[Image:Platinum-Iridium meter bar.jpg|right|thumb|220px|Historical ''[[international prototype of the metre]]'', made of an alloy of platinum and iridium, that was the standard from 1889 to 1960.]]Although the new standard metre had the same value as the old metre, it had an "X" cross-section designed by [[Henri Tresca]] rather than a rectangular cross-section as this reduced the flexing when taking measurements. Moreover, the new bar, rather than being exactly one metre in length was a little longer than one metre and had lines engraved on them that were exactly one metre apart.<ref>
{{cite book |first1=Thomas |last1=McGreevy |title=The Basis of Measurement: Volume 1 – Historical Aspects |pages=150–151 |isbn=0-948251-82-4 |year=1995 |publisher=Pitcon Publishing (Chippenham) Ltd}}
</ref> The London firm [[Johnson Matthey]] delivered 30 prototype metres and 40 prototype kilograms. At the first meeting of the [[CGPM]] in 1889 bar No.&nbsp;6 and cylinder No.&nbsp;X were chosen by lot as the international prototypes. The remainder were either kept as BIPM working copies or distributed by lot to member states as national prototypes.<ref>
{{cite journal
 |last1= Jabbour
 |first1= Z.J.
 |last2= Yaniv
 |first2= S.L.
 |year= 2001
 |title= The Kilogram and Measurements of Mass and Force
 |journal= J. Res. Natl. Inst. Stand. Technol.
 |volume= 106
 |issue= 1
 |pages= 25–46
 |url= http://nvl.nist.gov/pub/nistpubs/jres/106/1/j61jab.pdf
 |access-date= 28 March 2011
 |doi= 10.6028/jres.106.003
 |pmid= 27500016
 |pmc= 4865288
 |archive-url= https://web.archive.org/web/20110604144310/http://nvl.nist.gov/pub/nistpubs/jres/106/1/j61jab.pdf
 |archive-date= 4 June 2011
 |url-status= dead
}}</ref>

The comparison of the new prototypes of the metre with each other involved the development of special measuring equipment and the definition of a reproducible temperature scale. The BIPM's [[Temperature measurement|thermometry]] work led to the discovery of special alloys of iron–nickel, in particular [[invar]], whose practically negligible coefficient of expansion made it possible to develop simpler baseline measurement methods,<ref name="Guillaume-1906">{{Cite journal |last=Guillaume |first=C.-H.-Ed |date=1906-01-01 |title=La mesure rapide des bases géodésiques |url=https://zenodo.org/record/2007289 |journal=Journal de Physique Théorique et Appliquée |volume=5 |pages=242–263 |doi=10.1051/jphystap:019060050024200}}</ref> and for which its director, the Swiss physicist [[Charles Édouard Guillaume]], was granted the [[Nobel Prize in Physics]] in 1920. Guillaume's Nobel Prize marked the end of an era in which [[metrology]] was leaving the field of [[geodesy]] to become an autonomous [[Branches of science|scientific discipline]] capable of redefining the metre through [[Technology|technological]] applications of [[physics]].<ref>{{Cite web |title=BIPM – la définition du mètre |url=https://www.bipm.org/fr/measurement-units/history-si/evolution_metre.html |archive-url=https://web.archive.org/web/20170430075245/http://www.bipm.org/fr/measurement-units/history-si/evolution_metre.html |archive-date=30 April 2017 |access-date=2019-05-15 |website=www.bipm.org}}</ref><ref name="BIPM-150">{{Cite web |title=History – The BIPM 150 |url=https://thebipm150.org/history/ |access-date=2025-01-24 |language=}}</ref> On the other hand, the foundation of the United States Coast and Geodetic Survey by Ferdinand Rudolph Hassler paved the way to a new definition of the metre, with [[Charles Sanders Peirce]] being the first to experimentally link the metre to the wavelength of a spectral line. [[Albert A. Michelson]] soon took up the idea and improved it.<ref name="Crease-2009">{{Cite journal |last=Crease |first=Robert P. |date=2009-12-01 |title=Charles Sanders Peirce and the first absolute measurement standard |url=https://pubs.aip.org/physicstoday/article/62/12/39/390647/Charles-Sanders-Peirce-and-the-first-absolute |journal=Physics Today |volume=62 |issue=12 |pages=39–44 |bibcode=2009PhT....62l..39C |doi=10.1063/1.3273015 |issn=0031-9228}}</ref>

The prototype metre was retained as the international standard until 1960 when the metre was redefined in terms of the wavelength of the orange-red line of [[krypton-86]]. The current definition of the metre is "the length of the path travelled by light in vacuum during a time interval of 1/{{val|299792458}} of a second".

On 16 November 2018, the 26th [[General Conference on Weights and Measures]] (CGPM) voted unanimously in favour of revised definitions of some [[SI base unit]]s, in particular the kilogram.<ref>{{Cite news|url=https://www.nist.gov/news-events/news/2018/11/historic-vote-ties-kilogram-and-other-units-natural-constants|title=Historic Vote Ties Kilogram and Other Units to Natural Constants|last=Materese|first=Robin|date=16 November 2018|work=NIST|access-date=17 November 2018|archive-date=18 November 2018|archive-url=https://web.archive.org/web/20181118014932/https://www.nist.gov/news-events/news/2018/11/historic-vote-ties-kilogram-and-other-units-natural-constants|url-status=live}}</ref> The new definitions came into force on 20 May 2019, but did not change the metre.<ref name=SI-statement/><ref name=bipm>[http://www.bipm.org/en/committees/cipm/meeting/105.html "Decision CIPM/105-13 (October 2016)"] {{Webarchive|url=https://web.archive.org/web/20170824095943/http://www.bipm.org/en/committees/cipm/meeting/105.html |date=24 August 2017 }}. The day is the 144th anniversary of the Metre Convention.</ref>

=== International organization ===
The Convention created an [[international organization]] with two governing organs to facilitate the standardization of weights and measures around the world. The first, the CGPM provides a forum for representative of member states, the second, the CIPM is an advisory committee of metrologists of high standing. The Secretariat or Headquarters provides appropriate meeting and laboratory facilities in support of the CGPM and CIPM.<ref name=":2">
{{cite web
 |url=http://www.bipm.org/en/convention/
 |title=The Metre Convention
 |publisher=Bureau International des Poids et Mesures
 |access-date=1 October 2012
 |archive-date=26 September 2012
 |archive-url=https://web.archive.org/web/20120926202046/http://www.bipm.org/en/convention/
 |url-status=live
}}</ref>

The structure may be compared to a [[corporation]], the CIPM is analogous to a [[board of directors]], and the CGPM to a [[shareholders' meeting]].

==== General Conference on Weights and Measures ====
The [[General Conference on Weights and Measures]] ({{lang|fr|Conférence générale des poids et mesures}} or CGPM) is the principal decision-making body put on place by the convention. It is made up of delegates from member states and [non-voting] observers from associate states and economies.<ref>
{{cite web
 |url         = http://www.bipm.org/en/convention/cgpm/
 |title       = General Conference on Weights and Measures
 |year        = 2011
 |publisher   = Bureau International des Poids et Mesures
 |access-date  = 26 September 2012
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20120926233323/http://www.bipm.org/en/convention/cgpm/
 |archive-date = 26 September 2012
}}</ref> The conference usually meets every four years to receive and discuss a report from the CIPM and to endorse new developments in the SI on the advice of the CIPM though at the 2011 meeting, it agreed to meet again in 2014 rather than 2015 to discuss the maturity of the [[New SI definitions|new SI proposals]].<ref name="bipm.org">
{{cite press release
 | url = http://www.bipm.org/utils/en/pdf/Press_release_resolution_1_CGPM.pdf
 | title = General Conference on Weights and Measures approves possible changes to the International System of Units, including redefinition of the kilogram.
 | publisher = [[General Conference on Weights and Measures]]
 | location = Saint-Cloud, France
 | date = 23 October 2011
 | access-date = 25 October 2011
 | archive-date = 9 February 2012
 | archive-url = https://web.archive.org/web/20120209175127/http://www.bipm.org/utils/en/pdf/Press_release_resolution_1_CGPM.pdf
 | url-status = live
}}</ref> It is also responsible for new appointments to the CIPM and decides on major issues concerning the development and financing of the BIPM. According to the Metre Convention (Art. 4) the President of the [[French Academy of Sciences]] is also the President of the General Conference on Weights and Measures.

==== International Committee for Weights and Measures ====
[[File:Metric seal.svg|thumb|200px|Seal of the BIPM]]
The [[General Conference on Weights and Measures#CIPM|International Committee for Weights and Measures]] ({{lang|fr|Comité international des poids et mesures}} or CIPM) is made up of eighteen (originally fourteen)<ref>Convention of the Metre (1875), Appendix 1 (Regulation), Article 8</ref> individuals from a member state of high scientific standing, nominated by the CGPM to advise the CGPM on administrative and technical matters. It is responsible for the running of ten consultative committees (CCs), each of which investigates different aspects of metrology – one CC discusses the measurement of temperature, another the measurement of mass and so on. The CIPM meets annually at Saint-Cloud to discuss annual reports from the various CCs, to submit an annual report to the governments of member states in respect of the administration and finances of the BIPM and to advise the CGPM on technical matters as and when necessary. Each member of the CIPM is from a different member state – with France, in recognition of its work in setting up the convention, always having one seat on the CIPM.<ref>
{{cite web
 |url = http://www.bipm.org/en/committees/cipm/
 |title = CIPM: International Committee for Weights and Measures
 |year = 2011
 |publisher = Bureau International des Poids et Mesures
 |access-date = 26 September 2012
 |archive-date = 24 September 2012
 |archive-url = https://web.archive.org/web/20120924192125/http://www.bipm.org/en/committees/cipm/
 |url-status = live
}}</ref><ref>
{{cite web|url=https://www.bipm.org/en/about-us/member-states/fr/|title=BIPM – France [Member State]|website=bipm.org|access-date=5 January 2018|archive-date=6 January 2018|archive-url=https://web.archive.org/web/20180106072343/https://www.bipm.org/en/about-us/member-states/fr/|url-status=dead}}</ref>

==== Secretariat of the BIPM ====
The Secretariat (or Headquarters) of the [[International Bureau of Weights and Measures]] ({{lang|fr|Bureau international des poids et mesures}} or BIPM) is based at Saint-Cloud, France. It has custody of the now historical [[international prototype of the kilogram]] and provides [[metrology]] services for Member States and hosts  formal meetings. It also has custody of the former [[international prototype of the metre]] which was retired in 1960. Over the years the various prototypes of the metre and of the kilogram were returned to the BIPM laboratories for recalibration services.

Initially it had a staff of 9, falling to 4 once the initial batch of prototypes had been distributed;<ref>Convention of the Metre (1875), Appendix 1 (Regulation), Article 6</ref> in 2012 it had a staff of over 70 people and an annual budget of over €10&nbsp;million.<ref>
{{cite web
 |url = http://www.bipm.org/en/bipm/
 |title = The BIPM headquarters
 |year = 2011
 |publisher = Bureau International des Poids et Mesures
 |access-date = 26 September 2012
 |archive-date = 7 November 2012
 |archive-url = https://web.archive.org/web/20121107000551/http://www.bipm.org/en/bipm/
 |url-status = live
}}</ref> The director of the BIPM is ''ex-officio'' a member of the CIPM and a member of all consultative committees.

=== Headquarters, language and protocol ===
[[File:BIPM courtyard.jpg|thumb|upright=1.35|The [[Pavillon de Breteuil]] in [[Saint-Cloud]], Paris]]
The original treaty was written in French and the authoritative language of all official documents is French. Communication between the BIPM and member states is, in the case of France, via the French Foreign Minister and in the case of all other members, via the members' ambassador to France.<ref>Convention of the Metre, Appendix 1 (Regulations), Articles 16 and 19</ref>

The French government offered the treaty members the [[Pavillon de Breteuil]] in [[Saint-Cloud]] to house the BIPM. The Pavillon was originally built in 1675 on the estate of the Château de Saint-Cloud which was home to, amongst others, [[Napoleon III|Emperor Napoleon III]]. The château was all but destroyed during the [[Franco-Prussian War]] (1870–1) and the Pavillon badly damaged.<ref>
{{cite web
 |title = The BIPM headquarters
 |url = http://www.bipm.org/en/bipm/
 |access-date = 27 September 2012
 |publisher = [[International Bureau of Weights and Measures]]
 |archive-date = 7 November 2012
 |archive-url = https://web.archive.org/web/20121107000551/http://www.bipm.org/en/bipm/
 |url-status = live
}}</ref> The Pavillon has been fully restored and, as headquarters of an [[intergovernmental organization]] enjoys privileges and immunities.<ref>
{{cite web
 |title = Protocol
 |url = http://www.diplomatie.gouv.fr/en/spip.php?page=article_imprim&id_article=15045
 |access-date = 27 September 2012
 |publisher = [[Ministry of Foreign and European Affairs (France)|Ministère Affaires étrangères, Republique Francaise]] [Ministry of Foreign Affairs, Republic of France]
 |date = 10 January 2011
 |archive-date = 3 April 2013
 |archive-url = https://web.archive.org/web/20130403093934/http://www.diplomatie.gouv.fr/en/spip.php?page=article_imprim&id_article=15045
 |url-status = live
}}</ref>

== Post-1875 developments ==
The science of metrology has progressed vastly since 1875. In particular the treaty was amended in 1921 with the result that many other international organizations have a forum within the CIPM to ensure harmonization of measurement standards across many [[Academic discipline|disciplines]]. In addition, what were originally conceived as standards for the purposes of trade have now been extended to cover a large number of aspects of human activity including medicine, science, engineering and technology.

=== Extensions to the treaty (1921) and development of the SI ===
{{main|International System of Units}}

The metre convention was originally drawn up with the main purpose of providing standards of length and mass only.  Standards relating to other quantities were under the control of other bodies – time was measured by [[astronomer]]s, electrical units by a series of ad-hoc international conferences,<ref>
{{cite web
 |title = System of Measurement Units
 |date = 24 April 2012
 |url = http://www.ieeeghn.org/wiki/index.php/System_of_Measurement_Units
 |access-date = 1 October 2012
 |publisher = [[IEEE]]
 |archive-date = 21 August 2014
 |archive-url = https://web.archive.org/web/20140821025655/http://www.ieeeghn.org/wiki/index.php/System_of_Measurement_Units
 |url-status = live
}}</ref> and other physical standards and concepts were maintained or defined by international bodies such as [[International Congress of Applied Chemistry]] or the [[International Union of Pure and Applied Physics]].

In 1901 [[Giovanni Giorgi|Giorgi]] published a proposal for building a coherent set of units based on four base units – the metre, kilogram, second and one electrical unit ([[ampere]], [[volt]] or [[ohm]]). In 1921 the convention was extended to permit the promotion of standards relating to any physical quantity which greatly increased the scope of the CIPM's remit and implicitly giving it freedom to exploit Giorgi's proposals. The 8th CGPM (1933) resolved to work with other international bodies to agree to standards for electrical units that could be related back to the international prototypes.<ref>
{{cite web
 |url = http://www.bipm.org/en/CGPM/db/8/10/
 |title = Résolution 10 de la 8e réunion de la CGPM (1933) – Substitution des unités électriques absolues aux unités dites " internationales "
 |trans-title = Resolution 10 of the 8th meeting of the CGPM (1933) – Substitution of the so-called "International" electrical units by absolute electrical units
 |language = fr
 |year = 1935
 |publisher = Bureau International des Poids et Meseures
 |access-date = 2 October 2012
 |archive-date = 26 November 2020
 |archive-url = https://web.archive.org/web/20201126185709/https://www.bipm.org/en/CGPM/db/8/10/
 |url-status = live
}}</ref> This was agreed in principle by the International Electrotechnical Commission at its congress in Brussels in 1935 subject to the choice of the fourth unit being agreed with, amongst others, the appropriate consultative committee of the CIPM.<ref>
{{cite journal
 |first = Arthur E
 |last = Kennelly
 |title = Adoption of the Metre-Kilogram-Mass-Second (M.K.S.) Absolute System of Practical Units by the International Electrotechnical Commission (I.E.C.), Bruxelles, June 1935
 |journal = Proceedings of the National Academy of Sciences of the United States of America
 |date = 21 October 1935
 |volume = 21
 |number = 10
 |pages = 579–583
 |doi=10.1073/pnas.21.10.579|pmid = 16577693
 |bibcode = 1935PNAS...21..579K
 |pmc = 1076662
 |doi-access = free
}}</ref>

In 1948, three years after the end of [[World War II]] and fifteen years after the 8th CGPM, the 9th CGPM was convened. In response to formal requests made by the International Union of Pure and Applied Physics and by the French Government to establish a practical system of units of measure, the CGPM requested the CIPM to prepare recommendations for a single practical system of units of measurement, suitable for adoption by all countries adhering to the Metre Convention.<ref>
{{cite conference
 |url = http://www.bipm.org/en/CGPM/db/9/6/
 |title = Resolution 6 – Proposal for establishing a practical system of units of measurement
 |conference = 9th Conférence Générale des Poids et Mesures (CGPM)
 |date = 12–21 October 1948
 |access-date = 8 May 2011
 |archive-date = 14 May 2013
 |archive-url = https://web.archive.org/web/20130514081152/http://www.bipm.org/en/CGPM/db/9/6/
 |url-status = live
}}</ref> At the same time the CGPM formally adopted a recommendation for the writing and printing of unit symbols and of numbers.<ref>
{{cite conference
 |url = http://www.bipm.org/en/CGPM/db/9/7/
 |title = Resolution 7 – Writing and printing of unit symbols and of numbers
 |conference = 9th Conférence Générale des Poids et Mesures (CGPM)
 |date = 12–21 October 1948
 |access-date = 8 May 2011
 |archive-date = 28 July 2012
 |archive-url = https://web.archive.org/web/20120728105127/http://www.bipm.org/en/CGPM/db/9/7/
 |url-status = live
}}</ref> The recommendation also catalogued the recommended symbols for the most important [[MKS system of units|MKS]] and [[Centimetre gram second system of units|CGS]] units of measure and for the first time the CGPM made recommendations concerning derived units.

The CIPM's draft proposal, which was an extensive revision and simplification of the metric unit definitions, symbols and terminology based on the MKS system of units, was put to the 10th CGPM in 1954. In the proposal the CIPM recommended that the ampere be the base unit from which electromechanical standards would be derived. After negotiations with the CIS and IUPAP, two further base units, the degree kelvin and the candela were also proposed as base units.<ref>
{{cite conference
 |url = http://www.bipm.org/en/CGPM/db/10/6/
 |title = Resolution 6 – Practical system of units
 |conference = 10th Conférence Générale des Poids et Mesures (CGPM)
 |date = 5–14 October 1954
 |access-date = 8 May 2011
 |archive-date = 1 April 2021
 |archive-url = https://web.archive.org/web/20210401081328/https://www.bipm.org/en/CGPM/db/10/6/
 |url-status = live
}}</ref> The full system and name "Système international d'unités" were adopted at the 11th CGPM.<ref>
{{cite conference
 |url = http://www.bipm.org/en/CGPM/db/11/12/
 |title = Resolution 12 – Système international d'unités
 |conference = 11th Conférence Générale des Poids et Mesures (CGPM)
 |date = 11–20 October 1960
 |access-date = 8 May 2011
 |archive-date = 14 May 2013
 |archive-url = https://web.archive.org/web/20130514081801/http://www.bipm.org/en/CGPM/db/11/12/
 |url-status = live
}}</ref> During the years that followed the definitions of the base units and particularly the {{lang|fr|mise en pratique}}<ref>
{{cite web
 |url = http://www.bipm.org/en/si/si_brochure/appendix2/
 |title = Practical realisation of the definitions of some important units
 |work = SI brochure, Appendix 2
 |publisher = BIPM
 |date = 9 September 2010
 |access-date = 5 May 2011
 |archive-date = 10 August 2014
 |archive-url = https://web.archive.org/web/20140810093615/http://www.bipm.org/en/si/si_brochure/appendix2/
 |url-status = live
}}</ref> to realize these definitions have been refined.

The formal definition of International System of Units (SI) along with the associated resolutions passed by the CGPM and the CIPM are published by the BIPM on the Internet and in brochure form at regular intervals. The eighth edition of the brochure ''Le Système international d'unités – The International System of Units'' was published in 2006.<ref>{{SIbrochure8th}}</ref>

=== Mutual Recognition Arrangements (CIPM-MRA) ===
[[File:CIPM-MRA-logo.jpg|thumb|Logo used by laboratories that have been accredited under the CIPM MRA scheme]]
During the 1940s, the United States government recognized the benefits of its suppliers keeping [[quality control]] records in respect of manufactured goods that would provide traceability of the process. This process was formalized by the British Government and in 1979 as the quality control standard [[BS 5750|BS&nbsp;5750]]. In 1987 BS&nbsp;5750 was adopted by [[International Organization for Standardization|ISO]] as the basis for [[ISO 9000]].<ref>
{{cite web
 |url = http://www.bsieducation.org/Education/HE/quality-management/quality-management.shtml
 |title = BSI Education: Quality Management Systems
 |access-date = 2 October 2012
 |year = 2008
 |publisher = [[British Standards Institution]] (BSI)
 |archive-date = 25 February 2012
 |archive-url = https://web.archive.org/web/20120225061350/http://www.bsieducation.org/Education/HE/quality-management/quality-management.shtml
 |url-status = live
}}</ref> ISO 9000 is a general purpose quality control standard which works in conjunction industry-specific standards: for example ISO 15195:2003 which gives the specific requirements for reference measurement laboratories in laboratory medicine.<ref>
{{cite web
 |url = http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=38363
 |title = ISO 15195:2003 – Laboratory medicine – Requirements for reference measurement laboratories
 |publisher = [[International Organization for Standardization]] (ISO)
 |access-date = 2 October 2012
 |archive-date = 8 May 2016
 |archive-url = https://web.archive.org/web/20160508155108/http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=38363
 |url-status = live
}}</ref>

International trade is hampered by one country not recognising the quality controls in place in other countries – often due to standards being different or being incompatible with each other. At the 20th CGPM (1995), it was recognized that although ad-hoc recognition of instrument calibration between cooperating countries had been taking place for a hundred years, a need had arisen for a more comprehensive agreement. Consequently, the CIPM was mandated to investigate the setting up of a [[Mutual Recognition Agreement]] in respect of instrument calibration. Any such agreement would require the keeping of records that could demonstrate the traceability of calibrations back to the base standards. Such records would be recorded within an ISO&nbsp;9000 framework. Four years later, in 1999 the text of the CIPM-MRA was agreed at the 21st CGPM.<ref>
{{cite web
 |url = http://www.bipm.org/en/cipm-mra/historical.html
 |title = Historical development of the CIPM MRA
 |access-date = 2 October 2012
 |publisher = [[International Bureau of Weights and Measures|Bureau International des Poids et Mesures]]
 |archive-date = 19 September 2012
 |archive-url = https://web.archive.org/web/20120919144100/http://www.bipm.org/en/cipm-mra/historical.html
 |url-status = live
}}</ref><ref>
{{cite web
 |url = http://www.bipm.org/en/cipm-mra/mra_online.html
 |title = Text of the CIPM MRA
 |access-date = 15 October 2012
 |publisher = [[International Bureau of Weights and Measures|Bureau International des Poids et Mesures]]
 |year = 2003
 |archive-date = 19 September 2012
 |archive-url = https://web.archive.org/web/20120919143925/http://www.bipm.org/en/cipm-mra/mra_online.html
 |url-status = live
}}</ref>

The CIPM-MRA scheme is to catalogue the capabilities of National Measurement Institutes (NMIs) such as [[National Institute of Standards and Technology|NIST]] in the United States or the [[National Physical Laboratory (United Kingdom)|National Physical Laboratory]] in Britain whose calibration procedures have been peer-assessed. The essential points of CIPM-MRA are:<ref>
{{cite web
 |url = http://www.bipm.org/en/cipm-mra/objectives.html
 |title = The essential points of the CIPM MRA
 |publisher = [[International Bureau of Weights and Measures|Bureau International des Poids et Mesures]]
 |access-date = 2 October 2012
 |archive-date = 19 September 2012
 |archive-url = https://web.archive.org/web/20120919144035/http://www.bipm.org/en/cipm-mra/objectives.html
 |url-status = live
}}</ref>
* The agreement is only open to countries that have signed the Metre Convention, either as full or as associate members.
* A country may have more than one NMI, though only one NMI is chosen as the signatory organization.
* The measurement capabilities of NMIs will be peer-reviewed at regular intervals and each NMI will recognize the measurement capabilities of other NMIs.
* The BIPM maintains a publicly available database of the measurement capabilities of each NMI.
* NMIs

Subsequent to launch of the CIPM MRA and in response to a [[European Community]] [[Directive (European Union)|directive]] on {{lang|la|in vitro}} medical devices,<ref>{{CELEX|31998L0079|text=Directive 98/79/EC of the European Parliament and of the Council of 27 October 1998 on in vitro diagnostic medical devices}}</ref> the [[Joint Committee for Traceability in Laboratory Medicine]] (JCTLM) was created in 2002 through a Declaration of Cooperation between the International Committee of Weights and Measures (CIPM), the [[International Federation of Clinical Chemistry and Laboratory Medicine]] (IFCC), and the [[International Laboratory Accreditation Cooperation]] (ILAC).<ref>
{{cite web
 |url = http://www.bipm.org/en/committees/jc/jctlm/
 |title = JCTLM: Joint Committee for Traceability in Laboratory Medicine
 |publisher = [[International Bureau of Weights and Measures|Bureau International des Poids et Mesures]]
 |access-date = 2 October 2012
 |archive-date = 16 May 2012
 |archive-url = https://web.archive.org/web/20120516010132/http://www.bipm.org/en/committees/jc/jctlm/
 |url-status = live
}}</ref> The joint committee provides a forum for the harmonization of standards of the various participants.

=== Coordination of International Atomic Time ===
With the advent of the [[atomic clock]] it has been possible to define and measure [[International Atomic Time]] with sufficient precision that variations in the [[Earth's rotation]] can be detected. The [[International Earth Rotation and Reference Systems Service|International Earth Rotation Service]] monitors these changes relative to the stars at regular intervals and proposes leap seconds as and when these are needed. Currently there are over 200 atomic clocks in over 50 national laboratories around the world and the BIPM, in terms of the mandate given to it under the Metre Convention, coordinates the various atomic clocks.<ref>
{{cite web
 |url = http://www.bipm.org/en/scientific/tai/tai.html
 |title = International Atomic Time
 |publisher = [[International Bureau of Weights and Measures|Bureau International des Poids et Mesures]]
 |access-date = 21 October 2012
 |archive-url = https://web.archive.org/web/20110110113226/http://www.bipm.org/en/scientific/tai/tai.html
 |archive-date = 10 January 2011
 |url-status = dead
}}</ref>

=== New SI ===
{{Main|2019 revision of the SI}}
[[File:Relations between New SI units definitions.svg|thumb|250px|Relations between 2019 definitions of SI units (in colour) and with seven fundamental constants of nature (in grey) with fixed numerical values.]]
After 1960, when the definition of the metre was linked to a particular wavelength of light rather than the international prototype of the metre, the only unit of measure that remained dependent on a particular artefact was the kilogram. Over the years, small drifts which could be as high as {{gaps|20|×|10<sup>−9</sup>}} kilograms per annum in the mass of the international prototype of the kilogram were detected.<ref>
{{cite web
 |url = http://physics.vniim.ru/SI50/files/mohr.pdf
 |author = Peter Mohr
 |title = Recent progress in fundamental constants and the International System of Units
 |work = Third Workshop on Precision Physics and Fundamental Physical Constants
 |date = 6 December 2010
 |access-date = 2 January 2011
 |archive-url = https://web.archive.org/web/20110824105816/http://physics.vniim.ru/SI50/files/mohr.pdf
 |archive-date = 24 August 2011
 |url-status = dead
}}</ref> At the 21st meeting of the CGPM (1999), national laboratories were urged to investigate ways of breaking the link between the kilogram and a specific artefact.

Independently of this drift having been identified, the [[Avogadro constant#International Avogadro Coordination|Avogadro project]] and development of the [[Kibble balance|Kibble (or watt) balance]] promised methods of indirectly measuring mass with a very high precision. These projects provided tools that enabled alternative means of redefining the kilogram.<ref name=Crease>
{{cite journal
 |url = http://physicsworld.com/cws/article/indepth/2011/mar/22/metrology-in-the-balance
 |title = Metrology in the balance
 |first1 = Robert P
 |last1 = Crease
 |access-date = 28 June 2012
 |journal = Physics World
 |volume = 24
 |issue = 3
 |pages = 39–45
 |date = 22 March 2011
 |bibcode = 2011PhyW...24c..39C
 |doi = 10.1088/2058-7058/24/03/34
 |archive-date = 27 April 2020
 |archive-url = https://web.archive.org/web/20200427013941/https://physicsworld.com/a/metrology-in-the-balance/
 |url-status = live
}}</ref>

A report published in 2007 by the Consultative Committee for Thermometry to the CIPM noted that their definition of temperature had proved to be unsatisfactory for temperatures below 20&nbsp;K and for temperatures above 1300&nbsp;K. The committee was of the view that the [[Boltzmann constant]] provided a better basis for temperature measurement than did the [[triple point]] of water, as it overcame these difficulties.<ref>
{{cite web
 |url = http://www.bipm.org/wg/CCT/TG-SI/Allowed/Documents/Report_to_CIPM_2.pdf
 |title = Report to the CIPM on the implications of changing the definition of the base unit kelvin
 |author = Fischer, J.
 |date = 2 May 2007
 |access-date = 2 January 2011
 |display-authors = etal
 |archive-date = 23 November 2008
 |archive-url = https://web.archive.org/web/20081123054012/http://www.bipm.org/wg/CCT/TG-SI/Allowed/Documents/Report_to_CIPM_2.pdf
 |url-status = live
}}</ref>

Over the next few years the support for natural constants grew and details were clarified,<ref>
{{cite web
 |url         = http://www.iupap.org/ga/ga26/sunamcorpt.pdf
 |title       = Resolution proposal submitted to the IUPAP Assembly by Commission C2 (SUNAMCO)
 |publisher   = International Union of Pure and Applied Physics
 |year        = 2008
 |access-date  = 8 May 2011
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20110927085329/http://www.iupap.org/ga/ga26/sunamcorpt.pdf
 |archive-date = 27 September 2011
}}</ref><ref name="draft">
{{cite web
 |url = http://www.bipm.org/utils/en/pdf/si_brochure_draft_ch2.pdf
 |title = Draft Chapter 2 for SI Brochure, following redefinitions of the base units
 |author = Ian Mills
 |publisher = CCU
 |date = 29 September 2010
 |access-date = 1 January 2011
 |archive-date = 18 May 2020
 |archive-url = https://web.archive.org/web/20200518205720/https://www.bipm.org/utils/en/pdf/si_brochure_draft_ch2.pdf
 |url-status = live
}}</ref><ref>
{{cite web
 |url = http://www.bipm.org/utils/common/pdf/24_CGPM_Convocation_Draft_Resolution_A.pdf
 |title = On the possible future revision of the International System of Units, the SI – Draft Resolution A
 |publisher = [[General Conference on Weights and Measures#CIPM|International Committee for Weights and Measures]] (CIPM)
 |access-date = 14 July 2011
 |archive-date = 6 August 2011
 |archive-url = https://web.archive.org/web/20110806053509/http://www.bipm.org/utils/common/pdf/24_CGPM_Convocation_Draft_Resolution_A.pdf
 |url-status = live
}}</ref><ref>
{{cite conference
 |conference = 24th meeting of the General Conference on Weights and Measures
 |title = On the possible future revision of the International System of Units, the SI
 |url = http://www.bipm.org/utils/en/pdf/24_CGPM_Resolution_1.pdf
 |publisher = International Bureau for Weights and Measures
 |location = Saint-Cloud, France
 |date = 21 October 2011
 |access-date = 1 October 2012
 |archive-date = 13 January 2012
 |archive-url = https://web.archive.org/web/20120113072107/http://www.bipm.org/utils/en/pdf/24_CGPM_Resolution_1.pdf
 |url-status = live
}}</ref><ref name="bipm.org"/> until in November 2018, the 26th General Conference on Weights and Measures voted unanimously in favour of revised definitions of the [[SI base unit]]s.<ref>
{{cite web
 |url=https://www.nist.gov/news-events/news/2018/11/historic-vote-ties-kilogram-and-other-units-natural-constants
 |title=Historic Vote Ties Kilogram and Other Units to Natural Constants
 |publisher=NIST
 |date=16 November 2018
 |access-date=16 November 2018
 |archive-date=18 November 2018
 |archive-url=https://web.archive.org/web/20181118014932/https://www.nist.gov/news-events/news/2018/11/historic-vote-ties-kilogram-and-other-units-natural-constants
 |url-status=live
}}</ref><ref name=Milton16>
{{cite conference
 |conference=SIM XXII General Assembly
 |location=Montevideo, Uruguay
 |url=http://www.sim-metrologia.org.br/docs/2016Presentations/BIPM%202016.pdf#page=10
 |conference-url=http://www.sim-metrologia.org.br/docs/2016Presentations/
 |page=10
 |title=Highlights in the work of the BIPM in 2016
 |first=Martin
 |last=Milton
 |date=14 November 2016
 |access-date=21 November 2018
 |archive-url=https://web.archive.org/web/20170901031605/http://www.sim-metrologia.org.br/docs/2016Presentations/BIPM%202016.pdf#page=10
 |archive-date=1 September 2017
 |url-status=dead
}}</ref> The [[2019 revision of the SI]] came into force on the 144th anniversary of the convention, 20 May 2019.<ref name=SI-statement>
{{cite web
 |url = https://www.bipm.org/utils/common/pdf/SI-statement.pdf
 |title = BIPM statement: Information for users about the proposed revision of the SI
 |access-date = 5 May 2018
 |archive-url = https://web.archive.org/web/20180121160000/https://www.bipm.org/utils/common/pdf/SI-statement.pdf
 |archive-date = 21 January 2018
 |url-status = live
}}
</ref>
<ref>
{{cite web
 |url = http://www.bipm.org/en/committees/cipm/meeting/105.html
 |title = Decision CIPM/105-13 (October 2016)
 |access-date = 31 August 2017
 |archive-url = https://web.archive.org/web/20170824095943/http://www.bipm.org/en/committees/cipm/meeting/105.html
 |archive-date = 24 August 2017
 |url-status = live
}}</ref>

== Membership ==
The BIPM has two classes of adherents – full membership for those states that wish to participate in the activities of the BIPM and associate membership for those countries or economies<ref group = Note>As of 2012, the only "economy" that was an associate member was CARICOM (Caribbean Community) – its membership comprising [[Antigua and Barbuda]], [[Saint Kitts and Nevis]], [[Barbados]], [[Saint Lucia]], [[Belize]], [[Saint Vincent and the Grenadines]], [[Dominica]], [[Suriname]], [[Grenada]], [[Trinidad and Tobago]] and [[Guyana]]. [[Jamaica]], although also a member of CARICOM, is an associate of the CGPM in its own right.</ref> that only wish to participate in the [[Mutual recognition agreement|MRA]] programme. Associate members have observer status at the CGPM. Since all formal liaison between the convention organizations and national governments is handled by the member state's ambassador to France,<ref group = Note>In the case of France, the French Foreign Minister</ref> it is implicit that member states must have diplomatic relations with France,<ref>
{{cite web
 |url         = http://www.bipm.org/en/convention/cgpm/
 |title       = General Conference on Weights and Measures
 |year        = 2011
 |publisher   = Bureau International des Poids et Mesures
 |access-date  = 30 September 2012
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20120926233323/http://www.bipm.org/en/convention/cgpm/
 |archive-date = 26 September 2012
}}</ref> though during both world wars, nations that were at war with France retained their membership of the CGPM.<ref>
{{cite web
 |url = http://www.bipm.org/utils/en/pdf/CIPM-history-EN.pdf
 |title = Members of the International Committee for Weights and Measures (CIPM)
 |access-date = 3 October 2012
 |date = October 2011
 |publisher = Bureau International des Poids et Mesures
 |archive-date = 24 December 2013
 |archive-url = https://web.archive.org/web/20131224112652/http://www.bipm.org/utils/en/pdf/CIPM-history-EN.pdf
 |url-status = live
}}</ref> The opening session of each CGPM is chaired by the French foreign minister and subsequent sessions by the president of the [[French Academy of Sciences]].<ref>
{{cite web
 |url = http://www.french-metrology.com/en/international-activities/organisations/metre-convention.asp
 |title = The Metre Convention
 |publisher = La métrologie française
 |year = 2012
 |access-date = 3 October 2012
 |archive-date = 30 November 2012
 |archive-url = https://web.archive.org/web/20121130094602/http://www.french-metrology.com/en/international-activities/organisations/metre-convention.asp
 |url-status = dead
}}</ref>

On 20 May 1875 representatives from seventeen of countries that attended the Conference of the Metre in 1875, signed the Convention of the Metre.<ref group = Note>[[Argentina]], [[Austria-Hungary]], Belgium, [[Empire of Brazil|Brazil]], [[Denmark]], [[French Third Republic|France]], [[German Empire]], [[Kingdom of Italy|Italy]], [[Peru]], [[Kingdom of Portugal|Portugal]], [[Russian Empire|Russia]], [[Spain under the Restoration|Spain]], [[Sweden and Norway]], Switzerland, [[Ottoman Empire]], United States and [[Venezuela]].</ref> In April 1884 HJ Chaney, Warden of Standards in London unofficially contacted the BIPM inquiring whether the BIPM would calibrate some metre standards that had been manufactured in Britain. [[Ole Jacob Broch|Broch]], director of the BIPM replied that he was not authorized to perform any such calibrations for non-member states. On 17 September 1884, the British Government signed the convention.<ref name=":4">
{{cite book |last1=Quinn |first1=Terry |url=https://books.google.com/books?id=jlM907kFhcgC&q=metre++quinn+1883+cipm&pg=PA127 |title=From Artefacts to Atoms: The Bipm and the Search for Ultimate Measurement Standard |publisher=[[Oxford University Press]] |year=2012 |isbn=978-0-19-530786-3 |pages=8-12, 133–135}}</ref> This number grew to 21 in 1900, 32 in 1950, and 49 in 2001. {{As of|2024|10|16}}, the General Conference membership was made up of 64 member states, 37 associate states and economies and four international organizations as follows (with year of partnership between brackets):<ref>
{{cite web
 |url = http://www.bipm.org/en/about-us/member-states/
 |title = Member States
 |year = 2016
 |publisher = Bureau International des Poids et Mesures
 |access-date = 10 May 2017
 |archive-date = 15 January 2021
 |archive-url = https://web.archive.org/web/20210115093910/https://www.bipm.org/en/about-us/member-states/
 |url-status = live
}}</ref>

=== Member states ===
{| class="wikitable sortable"
|-
!Name
!Year of partnership
!Notes
|-
|Argentina
|1877
|
|-
|Australia
|1947
|
|-
|Austria
|1875
|Joined originally as [[Austria-Hungary]]
|-
|Belarus
|2020
|Belarus was previously an Associate member since 2003
|-
|Belgium
|1875
|
|-
|Brazil
|1921
|
|-
|Bulgaria
|1911
|
|-
|Canada
|1907
|
|-
|Chile
|1908
|
|-
|China
|1977
|
|-
|Colombia
|2013
|
|-
|Costa Rica
|2022
|
|-
|Croatia
|2008
|
|-
|Czech Republic
|1922
|Joined originally as part of [[Czechoslovakia]]
|-
|Denmark
|1875
|
|-
|Ecuador
|2019
|Ecuador was previously an Associate member since 2000
|-
|Egypt
|1962
|
|-
|Estonia
|2021
|
|-
|Finland
|1923
|
|-
|France
|1875
|
|-
|Germany
|1875
|Joined originally as the [[German Empire]]
|-
|Greece
|2001
|
|-
|Hungary
|1925
|
|-
|India
|1957
|
|-
|Indonesia
|1960
|
|-
|Iran
|1975
|
|-
|Iraq
|2013
|
|-
|Ireland
|1925
|Joined originally as the [[Irish Free State]]
|-
|Israel
|1985
|
|-
|Italy
|1875
|
|-
|Japan
|1885
|
|-
|Kazakhstan
|2008
|
|-
|Kenya
|2010
|
|-
|Lithuania
|2015
|
|-
|Malaysia
|2001
|
|-
|Mexico
|1890
|
|-
|Montenegro
|2018
|
|-
|Morocco
|2019
|
|-
|Netherlands
|1929
|
|-
|New Zealand
|1991
|
|-
|Norway
|1875
|Joined originally as part of [[Union between Sweden and Norway|Sweden and Norway]]
|-
|Pakistan
|1973
|
|-
|Poland
|1925
|
|-
|Portugal
|1876
|
|-
|Romania
|1884
|
|-
|Russian Federation
|1875
|Joined originally as the [[Russian Empire]]
|-
|Saudi Arabia
|2011
|
|-
|Serbia
|1879
|Joined as the [[Principality of Serbia]] in 1879, as the [[Kingdom of Yugoslavia]] in 1929, and as the [[Federal Republic of Yugoslavia]] in 2001<ref>{{cite web | url=http://www.bipm.org/en/convention/member_states/cs/ | title=The Republic of Serbia | publisher=BIPM official site | access-date=30 July 2014 | url-status=dead | archive-url=https://web.archive.org/web/20140808034802/http://www.bipm.org/en/convention/member_states/cs/ | archive-date=8 August 2014 }}</ref><ref>{{cite web | url=http://www.bipm.org/en/convention/member_states/yu/ | title=Serbia and Montenegro | publisher=BIPM official site | access-date=30 July 2014 | url-status=dead | archive-url=https://web.archive.org/web/20140808035358/http://www.bipm.org/en/convention/member_states/yu/ | archive-date=8 August 2014 }}</ref>
|-
|Singapore
|1994
|
|-
|Slovakia
|1922
|Joined originally as part of [[Czechoslovakia]]
|-
|Slovenia
|2016
|
|-
|South Africa
|1964<ref>{{Cite web |url=http://www.theheritageportal.co.za/article/short-history-metrication-movement-south-africa |title='''The Heritage Portal''' > ''A Short History of the Metrication Movement in South Africa'' The South African Bureau of Standards (SABS) announced on 15 September 1967 that a Metrication Advisory Board would be established to plan and co-ordinate the change-over to the metric system and a Metrication Department would be set up to implement its policies. There would be a ten-year grace period to allow industry and the general public to adjust. |access-date=8 January 2019 |archive-date=9 January 2019 |archive-url=https://web.archive.org/web/20190109012031/http://www.theheritageportal.co.za/article/short-history-metrication-movement-south-africa |url-status=live }}</ref>
|
|-
|South Korea
|1959
|
|-
|Spain
|1875
|
|-
|Sweden
|1875
|Joined originally as part of [[Union between Sweden and Norway|Sweden and Norway]]
|-
|Switzerland
|1875
|
|-
|Thailand
|1912
|
|-
|Tunisia
|2012
|
|-
|Turkey
|1875
|Joined originally as the [[Ottoman Empire]]
|-
|Ukraine
|2018
|
|-
|United Arab Emirates
|2015
|
|-
|United Kingdom
|1884
|
|-
|United States
|1878
|
|-
|Uruguay
|1908
|
|}

===Associates===
At its 21st meeting (October 1999), the CGPM created the category of "associate" for those states not yet members of the BIPM and for [[economic union]]s.<ref>BIPM official site: [http://www.bipm.org/en/convention/member_states/join_associate.html Procedure for a State or Economy to become an Associate of the General Conference] {{webarchive|url=https://web.archive.org/web/20140703100329/http://www.bipm.org/en/convention/member_states/join_associate.html |date=3 July 2014 }}</ref>
{| class="wikitable sortable"
|-
!Country
!Year of partnership
!Notes
|-
|Albania
|2007
|
|-
|Azerbaijan
|2015
|
|-
|Bangladesh
|2010
|
|-
|Bolivia
|2008
|
|-
|Bosnia and Herzegovina
|2011
|
|-
|Botswana
|2012
|
|-
|Cambodia
|2005
|
|-
|Caribbean Community
|2005
|
|-
|Chinese Taipei<ref>{{Cite web | url=https://www.bipm.org/en/about-us/associates/tw/ | title=BIPM – Chinese Taipei | access-date=4 November 2018 | archive-date=4 November 2018 | archive-url=https://web.archive.org/web/20181104170030/https://www.bipm.org/en/about-us/associates/tw/ | url-status=live }}</ref>
|2002
|
|-
|Cuba
|2000
|Suspended during 1 January 2022 – 15 October 2024<ref>{{Cite web |title=BIPM – Cuba |url=https://www.bipm.org/en/countries/cu |url-status=live |archive-url=https://web.archive.org/web/20241119084306/http://www.bipm.org/en/countries/cu |archive-date=19 November 2024 |access-date=6 December 2024 |publisher=BIPM}}</ref>
|-
|Ethiopia
|2018
|
|-
|Georgia
|2008
|
|-
|Ghana
|2009
|
|-
|Hong Kong
|2000
|
|-
|Jamaica
|2003
|
|-
|Kuwait
|2018
|
|-
|Latvia
|2001
|
|-
|Luxembourg
|2014
|
|-
|Malta
|2001
|
|-
|Mauritius
|2010
|
|-
|Republic of Moldova
|2007
|
|-
|Mongolia
|2013
|
|-
|Namibia
|2012
|
|-
|North Macedonia<ref>{{cite web |url=https://www.bipm.org/en/about-us/associates/mk/ |title=BIPM – North Macedonia |access-date=8 August 2019 |archive-date=8 August 2019 |archive-url=https://web.archive.org/web/20190808091414/https://www.bipm.org/en/about-us/associates/mk/ |url-status=live }}</ref>
|2006
|Joined as Macedonia
|-
|Oman
|2012
|
|-
|Panama
|2003
|
|-
|Paraguay
|2009
|
|-
|Peru
|2009
|
|-
|Philippines
|2002
|
|-
|Qatar
|2016
|
|-
|Sri Lanka
|2007
|
|-
|Syria
|2012
|
|-
|Tanzania
|2018
|
|-
|Uzbekistan
|2018
|
|-
|Vietnam
|2003
|
|-
|Zambia
|2010
|
|-
|Zimbabwe
|2010
|Suspended during 1 January 2021 – 8 February 2022<ref>{{Cite web |title=BIPM – Zimbabwe |url=https://www.bipm.org/en/countries/zw |url-status=live |archive-url=https://web.archive.org/web/20230929211517/https://www.bipm.org/en/countries/zw |archive-date=29 September 2023 |access-date=29 September 2023 |publisher=BIPM}}</ref>
|}

=== International organizations ===
The following international organizations have signed the CIPM MRA:
* [[International Atomic Energy Agency]] (IAEA), [[Vienna]], Austria (1999)
* [[Institute for Reference Materials and Measurements]] (IRMM), [[Geel]], Belgium (1999)
* [[World Meteorological Organization]] (WMO), [[Geneva]], Switzerland (2010)
* [[European Space Agency]] (ESA), Paris, France (2012)

=== Former member states ===
The following former members were excluded from the organization following failure to pay their arrears over a span of years and upon failing to provide any form of payment plan:<ref name=gimmemoney/>
* Cameroon was a member state from 1970<ref name="cgmp24" /> until 22 October 2012.<ref>International Bureau of Weights and Measures official site: [http://www.bipm.org/en/convention/member_states/cm/ The Republic of Cameroon] {{Webarchive|url=https://web.archive.org/web/20131029200002/http://www.bipm.org/en/convention/member_states/cm/ |date=29 October 2013 }}, retrieved 4 August 2013</ref>
* North Korea was a member state from 1982<ref>{{citation |last=Lord |first=John |title=Sizes: The Online Quantinary |location=Santa Monica |publisher=Sizes Inc |contribution-url=https://sizes.com/units/General/met_sys_spred.htm |contribution=Spread of the Metric System |date=2001 |access-date=6 June 2017 |archive-date=19 January 2019 |archive-url=https://web.archive.org/web/20190119175225/https://www.sizes.com/units/General/met_sys_spred.htm |url-status=live }}.</ref><ref name="cgmp24">[http://www.bipm.org/utils/common/pdf/CGPM/CGPM24.pdf#page=437 Proceedings of the 24th General Conference on Weights and Measures] {{Webarchive|url=https://web.archive.org/web/20201204110506/https://www.bipm.org/utils/common/pdf/CGPM/CGPM24.pdf#page=437 |date=4 December 2020 }}, 2011, page 437</ref> until 2012<ref name=gimmemoney>{{citation |url=http://www.bipm.org/utils/common/pdf/CGPM-2014/25th-CGPM-Report-of-CIPM-President-EN.pdf |publisher=International Bureau for Weights and Measures |title=Report of the President of the CIPM on the Work Accomplished since the 24th Meeting of the CGPM |date=November 2014 |page=5 |location=Saint-Cloud |access-date=6 June 2017 |archive-date=7 March 2019 |archive-url=https://web.archive.org/web/20190307202449/https://www.bipm.org/utils/common/pdf/CGPM-2014/25th-CGPM-Report-of-CIPM-President-EN.pdf |url-status=live }}.</ref>
* Dominican Republic was a member state from 1954<ref name="cgmp24" /> until 31 December 2014.<ref>{{cite web|title=– Dominican Republic [Member State]|url=http://www.bipm.org/en/about-us/member-states/do/|website=bipm.org|access-date=29 March 2017|archive-date=21 October 2018|archive-url=https://web.archive.org/web/20181021111444/https://www.bipm.org/en/about-us/member-states/do/|url-status=live}}</ref>
* Venezuela was a member state from 1879 until 14 November 2018.<ref>{{cite web | url=https://www.bipm.org/en/about-us/member-states/ve/ | title=The Bolivarian Republic of Venezuela | publisher=BIPM | access-date=31 October 2019 | archive-date=30 October 2019 | archive-url=https://web.archive.org/web/20191030232949/https://www.bipm.org/en/about-us/member-states/ve/ | url-status=dead }}</ref>
* Yemen was an associate from 21 July 2014 until 1 January 2018.<ref>{{Cite web | url=https://www.bipm.org/en/about-us/associates/ye/ | title=BIPM – Yemen | access-date=22 August 2018 | archive-date=23 August 2018 | archive-url=https://web.archive.org/web/20180823005844/https://www.bipm.org/en/about-us/associates/ye/ | url-status=dead }}</ref>
* Seychelles was an Associate from 10 September 2010 to 31 December 2021.<ref>{{Cite web |title=Former Associate: Seychelles |url=https://www.bipm.org/en/countries/sc |access-date=27 June 2024 |website=BIPM}}</ref>
* Sudan was an Associate from 26 June 2014 to 31 December 2021.<ref>{{Cite web |title=Former Associate: Sudan |url=https://www.bipm.org/en/countries/sd |access-date=27 June 2024}}</ref>

== See also ==
* [[Outline of metrology and measurement]]
* [[Metrication]]
* [[History of the metre]]
* [[Seconds pendulum]]
* [[World Metrology Day]]

== Notes ==
{{reflist|group = Note}}

== References ==
{{reflist}}

== Further reading ==
* {{cite EB1911|wstitle=Metric System |volume= 18}}
* Kershaw, Michael. "The 'nec plus ultra' of precision measurement: Geodesy and the forgotten purpose of the Metre Convention." ''Studies in History and Philosophy of Science Part A'' 43.4 (2012): 563–576. [http://lib.ifsu.edu.ph/ejournal/uploads/file/pdf/20180417_085957.pdf online]{{Dead link|date=December 2023 |bot=InternetArchiveBot |fix-attempted=yes }}
* Quinn, Terry. "The Metre Convention and world-wide comparability of measurement results." ''Accreditation and quality assurance'' 9.9 (2004): 533–538.
* Stigler, S. ''The History of Statistics: The Measurement of Uncertainty before 1900'' (1986).

== External links ==
{{commons category}}
{{wikisource}}
* [https://www.bipm.org/documents/20126/44107685/metre-convention.pdf Text of the current version of the Convention (in French with unofficial translation in English at the end)] {{Webarchive|url=https://web.archive.org/web/20211008110435/https://www.bipm.org/documents/20126/44107685/metre-convention.pdf |date=8 October 2021 }}
* [https://www.loc.gov/law/help/us-treaties/bevans/m-ust000001-0039.pdf Text in English, Library of Congress] {{Webarchive|url=https://web.archive.org/web/20170221161448/http://www.loc.gov/law/help/us-treaties/bevans/m-ust000001-0039.pdf |date=21 February 2017 }}
* [http://www.bipm.org/en/cipm-mra/mra_online.html Text of the CIPM-MRA agreement] {{Webarchive|url=https://web.archive.org/web/20120919143925/http://www.bipm.org/en/cipm-mra/mra_online.html |date=19 September 2012 }}

{{Systems of measurement}}
{{SI units}}

{{authority control}}

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