Decisions relating to the base units of the SI

SI Brochure, from Appendix 1

Length:

	1st CGPM, 1889	sanction of the prototype metre
	7th CGPM, 1927	definition and use of the prototype metre
	10th CGPM, 1954	metre adopted as a base unit
	11th CGPM, 1960	redefinition of the metre in terms of krypton 86 radiation
	15th CGPM, 1975	recommends value for the speed of light
	17th CGPM, 1983	redefinition of the metre using the speed of light, realization of the definition of the metre
	CIPM, 2002	specifies the rules for the practical realization of the definition of the metre
	CIPM, 2003	revision of the list of recommended radiations
	CIPM, 2005	revision of the list of recommended radiations
	CIPM, 2007	revision of the list of recommended radiations
	23rd CGPM, 2007	revision of the mise en pratique of the definition of the metre and development of new optical frequency standards
	CIPM, 2009	updates to the list of standard frequencies
	24th CGPM, 2011	on the possible future revision of the International System of Units, the SI
	24th CGPM, 2011	revision of the mise en pratique of the definition of the metre and development of new optical frequency standards
	CIPM, 2013	updates to the list of standard frequencies
	26th CGPM, 2018	revision of the International System of Units, the SI

We are pleased to present the 9th edition of the SI Brochure (2019), which defines and presents the Système International d'Unités, the SI (known in English as the International System of Units).