Editing Measurement (section)

== Standardization of measurement units ==
Measurements most commonly use the [[International System of Units]] (SI) as a comparison framework. The system defines seven [[SI base units|fundamental units]]: [[kilogram]], [[metre]], [[candela]], [[second]], [[ampere]], [[kelvin]], and [[mole (unit)|mole]]. All of these units are defined without reference to a particular physical object which would serve as a standard. Artifact-free definitions fix measurements at an exact value related to a [[physical constant]] or other invariable natural phenomenon, in contrast to reliance on standard artifacts which are subject to deterioration or destruction. Instead, the measurement unit can only ever change through increased accuracy in determining the value of the constant it is tied to.

[[File:SI base unit.svg|thumb|right|The seven base units in the SI system. Arrows point from units to those that depend on them.]]

The first proposal to tie an SI base unit to an experimental standard independent of fiat{{clarify|date=April 2025}} was by [[Charles Sanders Peirce]] (1839–1914),<ref>{{harvnb|Crease|2011|pp=182–4}}</ref> who proposed to define the metre in terms of the [[wavelength]] of a [[spectral line]].<ref>C.S. Peirce (July 1879) "Note on the Progress of Experiments for Comparing a Wave-length with a Metre" ''American Journal of Science'', as referenced by {{harvnb|Crease|2011|p=203 }}</ref> This directly influenced the [[Michelson–Morley experiment]]; Michelson and Morley cite Peirce, and improve on his method.<ref>{{cite book |last=Crease |first=Robert P. |date=2011 |title=World in the Balance: The Historical Quest for an Absolute System of Measurement |location=New York & London |publisher=W. W. Norton |isbn=978-0-393-34354-0 |page=203}}</ref>

=== Standards ===
{{see also|Metrology#Standards}}

With the exception of a few fundamental [[quantum]] constants, units of measurement are derived from historical agreements. Nothing inherent in nature dictates that an [[inch]] has to be a certain length, nor that a [[mile]] is a better measure of distance than a [[kilometre]]. Over the course of human history, however, first for convenience and then out of necessity, standards of measurement evolved so that communities would have certain common benchmarks. Laws regulating measurement were originally developed to prevent fraud in commerce.

[[Units of measurement]] are generally defined on a scientific basis, overseen by governmental or independent agencies, and established in international treaties, pre-eminent of which is the [[General Conference on Weights and Measures]] (CGPM), established in 1875 by the [[Metre Convention]], overseeing the International System of Units (SI).  For example, the metre was redefined in 1983 by the CGPM in terms of the speed of light, the kilogram was redefined in 2019 in terms of the [[Planck constant]] and the international yard was defined in 1960 by the governments of the United States, United Kingdom, Australia and South Africa as being ''exactly'' 0.9144 metres.

In the United States, the National Institute of Standards and Technology ([[NIST]]), a division of the [[United States Department of Commerce]], regulates commercial measurements. In the United Kingdom, the role is performed by the [[National Physical Laboratory (United Kingdom)|National Physical Laboratory]] (NPL), in Australia by the [[National Measurement Institute, Australia|National Measurement Institute]],<ref>{{cite web|url=http://www.measurement.gov.au/Pages/about.aspx |title=About Us |website=National Measurement Institute of Australia|date=3 December 2020 }}</ref> in South Africa by the [[Council for Scientific and Industrial Research]] and in India the [[National Physical Laboratory of India]].