Editing Metre Convention (section)

=== 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>