Editing International System of Units (section)

=== CGS and MKS systems ===

{{See also|CGS system of units}}
[[File:US National Length Meter.JPG|thumb|right|Closeup of the National Prototype Metre, serial number 27, allocated to the United States]]

The concept of a system of units emerged a hundred years before the SI.
In the 1860s, [[James Clerk Maxwell]], [[William Thomson, 1st Baron Kelvin|William Thomson]] (later Lord Kelvin), and others working under the auspices of the [[British Association for the Advancement of Science]], building on previous work of [[Carl Gauss]], developed the [[centimetre–gram–second system of units]] or cgs system in 1874. The systems formalised the concept of a collection of related units called a ''coherent'' system of units. In a coherent system, ''base units'' combine to define ''derived units'' without extra factors.<ref name=NIST330/>{{rp|page=2}} For example, using metre per second is coherent in a system that uses metre for length and second for time, but kilometre per hour is not coherent. The principle of coherence was successfully used to define a number of units of measure based on the CGS, including the [[erg]] for [[energy]], the [[dyne]] for [[force]], the [[barye]] for [[pressure]], the [[poise (unit)|poise]] for [[dynamic viscosity]] and the [[stokes (unit)|stokes]] for [[kinematic viscosity]].<ref name="BIPMCentenary">{{cite book |url=https://archive.org/details/internationalbur420page |page=[https://archive.org/details/internationalbur420page/page/12 12] |title=The International Bureau of Weights and Measures 1875–1975: NBS Special Publication 420 |date=20 May 1975 |editor-last1=Page
| editor-first1=Chester H. |editor-last2=Vigoureux |editor-first2=Paul |publisher=[[National Bureau of Standards]] | location=Washington, D.C.}}</ref>