Editing Metric system (section)

===Current===
The International System of Units is the modern metric system. It is based on the metre–kilogram–second–ampere (MKSA) system of units from early in the 20th century.<ref name=SI_units /> It also includes numerous coherent derived units for common quantities like power (watt) and irradience (lumen). Electrical units were taken from the International system then in use.  Other units like those for energy (joule) were modelled on those from the older CGS system, but scaled to be coherent with MKSA units. Two additional base units – the ''kelvin'', which is equivalent to degree Celsius for change in thermodynamic temperature but set so that 0&nbsp;K is [[absolute zero]], and the ''candela'', which is roughly equivalent to the [[international candle]] unit of illumination – were introduced. Later, another base unit, the ''mole'', a unit of [[amount of substance]] equivalent to the [[Avogadro number]] number of specified molecules, was added along with several other derived units.<ref name="Gold Book mole">{{Cite book |url=https://goldbook.iupac.org/terms/view/M03980 |title=IUPAC – mole (M03980) |author=IUPAC Gold Book |publisher=[[International Union of Pure and Applied Chemistry]]|doi=10.1351/goldbook.M03980 |s2cid=241546445 }}</ref>

The system was promulgated by the General Conference on Weights and Measures (French: ''Conférence générale des poids et mesures'' – CGPM) in 1960.  At that time, the metre was redefined in terms of the wavelength of a spectral line of the [[krypton-86]] atom (krypton-86 being a stable isotope of an inert gas that occurs in undetectable or trace amounts naturally), and the standard metre artefact from 1889 was retired.<ref name=":0">{{cite book|last1=Urone |first1=Peter Paul |last2=Hinrichs |first2=Roger |last3=Dirks |first3=Kim |last4=Sharma |first4=Manjula |title=College Physics |publisher=OpenStax |isbn=978-1-947172-01-2 |year=2020 |url=https://openstax.org/details/books/college-physics}}</ref>{{rp|16}}

Today, the International system of units consists of 7 base units and innumerable coherent derived units including 22 with special names. The last new derived unit, the ''katal'' for catalytic activity, was added in 1999. All the base units except the second are now defined in terms of exact and invariant constants of physics or mathematics, barring those parts of their definitions which are dependent on the second itself. As a consequence, the speed of light has now become an exactly defined constant, and defines the metre as {{frac|299,792,458}} of the distance light travels in a second. The kilogram was defined by a [[International Prototype of the Kilogram|cylinder of platinum-iridium alloy]] until a [[2019 revision of the SI#Kilogram|new definition]] in terms of  [[Physical constant|natural physical constants]] was adopted in 2019. As of 2022, the range of decimal prefixes has been extended to those for 10<sup>30</sup> (''quetta–'') and 10<sup>−30</sup> (''quecto–'').<ref>{{cite web |url=https://www.theregister.com/2022/11/22/new_si_prefixes_clear_the/|title=New SI prefixes clear the way for quettabytes of storage|date=22 November 2022|publisher=The Register|access-date=23 Nov 2022|df=dmy-all}}</ref>