Editing Base unit of measurement (section)

== International System of Units ==
{{main|SI base units|SI derived units}}
In the [[International System of Units]] (SI), there are seven base units: [[kilogram]], [[metre]], [[candela]], [[second]], [[ampere]], [[kelvin]], and [[mole (unit)|mole]].
Several derived units have been defined, many with special names and symbols.

In 2019 the seven SI base units were redefined in terms of seven defining constants. Therefore the SI base units are no longer necessary but were retained because for historical and practical reasons.<ref name=Brochure9_2019>{{cite web
 |title = 9th edition of the SI Brochure
 |publisher = BIPM
 |url = https://www.bipm.org/en/publications/si-brochure/
 |date = 2019
 |access-date = 20 May 2019
 |df = dmy-all
 |archive-date = 19 April 2021
 |archive-url = https://web.archive.org/web/20210419211921/https://www.bipm.org/en/publications/si-brochure
 |url-status = live
 }}</ref> See ''[[2019 revision of the SI]]''.