Editing Metrology (section)

===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"/>