Editing Metrology (section)

==Subfields==
Metrology is defined by the International Bureau of Weights and Measures (BIPM) as "the science of measurement, embracing both experimental and theoretical determinations at any level of uncertainty in any field of science and technology".<ref name="WhatIsBIPM">{{cite web|title=What is metrology?|url=http://www.bipm.org/en/worldwide-metrology/|publisher=BIPM|access-date=23 February 2017|ref=BIPMDef|url-status=live|archive-url=https://web.archive.org/web/20170324081343/http://www.bipm.org/en/worldwide-metrology/|archive-date=24 March 2017}}</ref> It establishes a common understanding of units, crucial to human activity.<ref name=FCM>{{cite book|url = http://resource.npl.co.uk/international_office/metrologyinshort.pdf|title = Metrology in Industry – The Key for Quality|publisher = [[International Society for Technology in Education|ISTE]]|author = Collège français de métrologie [French College of Metrology]|editor-first = Dominique|editor-last = Placko|year = 2006|isbn = 978-1-905209-51-4|url-status = live|archive-url = https://web.archive.org/web/20121023153656/http://resource.npl.co.uk/international_office/metrologyinshort.pdf|archive-date = 2012-10-23}}</ref> Metrology is a wide reaching field, but can be summarized through three basic activities: the definition of internationally accepted units of measurement, the realisation of these units of measurement in practice, and the application of chains of traceability (linking measurements to reference standards).<ref name=FCM/><ref name=C-S/> These concepts apply in different degrees to metrology's three main fields: scientific metrology; applied, technical or industrial metrology, and legal metrology.<ref name=C-S/>

===Scientific metrology===

Scientific metrology is concerned with the establishment of units of measurement, the development of new measurement methods, the realisation of measurement standards, and the transfer of traceability from these standards to users in a society.<ref name=FCM/><ref name = BGtoM/> This type of metrology is considered the top level of metrology which strives for the highest degree of accuracy.<ref name=FCM/> BIPM maintains a database of the metrological calibration and measurement capabilities of institutes around the world. These institutes, whose activities are peer-reviewed, provide the fundamental reference points for metrological traceability. In the area of measurement, BIPM has identified nine metrology areas, which are acoustics, electricity and magnetism, length, mass and related quantities, photometry and radiometry, ionizing radiation, time and frequency, thermometry, and chemistry.<ref>{{cite web  |url = http://kcdb.bipm.org/appendixc/  |title = The BIPM key comparison database  |publisher = BIPM  |access-date = 26 Sep 2013  |url-status = live  |archive-url = https://web.archive.org/web/20130928041400/http://kcdb.bipm.org/appendixc/  |archive-date = 2013-09-28  }}</ref>

As of May 2019 no physical objects define the base units.<ref>[http://www.bipm.org/en/committees/cipm/meeting/105.html Decision CIPM/105-13 (October 2016)]</ref> The motivation in the change of the base units is to make the entire system derivable from [[physical constants]], which required the removal of the prototype kilogram as it is the last artefact the unit definitions depend on.<ref name="SD">{{cite web|title=New measurement will help redefine international unit of mass: Ahead of July 1 deadline, team makes its most precise measurement yet of Planck's constant|url=https://www.sciencedaily.com/releases/2017/07/170701103514.htm|website=ScienceDaily|access-date=23 March 2018|language=en}}</ref> Scientific metrology plays an important role in this redefinition of the units as precise measurements of the physical constants is required to have accurate definitions of the base units. To redefine the value of a kilogram without an artefact the value of the [[Planck constant]] must be known to twenty parts per billion.<ref>{{cite web|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 = 23 March 2018|work = Physics World|publisher = [[Institute of Physics]]|date = 22 March 2011}}</ref> Scientific metrology, through the development of the [[Kibble balance]] and the [[Avogadro project]], has produced a value of Planck constant with low enough uncertainty to allow for a redefinition of the kilogram.<ref name="SD"/>

=== Applied, technical or industrial metrology ===

Applied, technical or industrial metrology is concerned with the application of measurement to manufacturing and other processes and their use in society, ensuring the suitability of measurement instruments, their calibration and quality control.<ref name=FCM/> Producing good measurements is important in industry as it has an impact on the value and quality of the end product, and a 10–15% impact on production costs.<ref name=C-S/> Although the emphasis in this area of metrology is on the measurements themselves, traceability of the measuring-[[Measuring instrument|device]] calibration is necessary to ensure confidence in the measurement. Recognition of the metrological competence in industry can be achieved through mutual recognition agreements, accreditation, or peer review.<ref name=C-S/> Industrial metrology is important to a country's economic and industrial development, and the condition of a country's industrial-metrology program can indicate its economic status.<ref name = "silva"/>

===Legal metrology===

Legal metrology "concerns activities which result from statutory requirements and concern measurement, [[Unit of measurement|units of measurement]], measuring instruments and methods of measurement and which are performed by competent bodies".<ref name=VIML>{{cite book|title=International Vocabulary of Terms in Legal Metrology |url=http://www.oiml.org/publications/V/V001-ef00.pdf |publisher=OIML |year=2000 |page=7 |location=Paris |url-status=dead |archive-url=https://web.archive.org/web/20070928030048/http://www.oiml.org/publications/V/V001-ef00.pdf |archive-date=September 28, 2007 }}</ref> Such statutory requirements may arise from the need for protection of health, public safety, the environment, enabling taxation, protection of consumers and fair trade. The International Organization for Legal Metrology ([[OIML]]) was established to assist in harmonising regulations across national boundaries to ensure that legal requirements do not inhibit trade.<ref name = "DeWayne">{{cite book|last1=Sharp|first1=DeWayne|title=Measurement, instrumentation, and sensors handbook|date=2014|publisher=CRC Press, Inc.|location=Boca Raton|isbn=978-1-4398-4888-3|edition=Second}}</ref> This harmonisation ensures that certification of measuring devices in one country is compatible with another country's certification process, allowing the trade of the measuring devices and the products that rely on them. [[WELMEC]] was established in 1990 to promote cooperation in the field of legal metrology in the [[European Union]] and among [[European Free Trade Association]] (EFTA) member states.<ref>{{cite web|last1=WELMEC Secretariat|title=WELMEC An introduction|url=http://www.welmec.org/fileadmin/user_files/publications/WELMEC-general/WELMEC_Guide_1-2016_-_WELMEC_An_introduction.pdf|publisher=WELMEC|access-date=28 February 2017|url-status=live|archive-url=https://web.archive.org/web/20170228165051/http://www.welmec.org/fileadmin/user_files/publications/WELMEC-general/WELMEC_Guide_1-2016_-_WELMEC_An_introduction.pdf|archive-date=28 February 2017}}</ref> In the United States legal metrology is under the authority of the Office of Weights and Measures of [[National Institute of Standards and Technology]] (NIST), enforced by the individual states.<ref name = "DeWayne"/>