BIPM - base units

Decisions relating to the base units of the SI

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Summary

Decisions relating to the establishment of the SI

Decisions relating to the base units of the SI

Decisions relating to SI derived and supplementary units

Decisions concerning terminology and the acceptance of units for use with the SI

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SI brochure, from Appendix 1

Length | Mass | Time | Electrical units
Thermodynamic temperature | Amount of substance | Luminous intensity

	1st CGPM, 1889	sanction of the prototype metre
	7th CGPM, 1927	definition and use of the prototype metre
	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

	1st CGPM, 1889	sanction of the prototype kilogram
	3rd CGPM, 1901	declaration on distinguishing mass and weight, and on the conventional value of g_n
	CIPM, 1967	declaration on applying prefixes to the gram
	21st CGPM, 1999	future redefinition of the kilogram

	CIPM, 1956	definition of the second as a fraction of the tropical year 1900
	11th CGPM, 1960	ratifies the CIPM 1956 definition of the second
	CIPM, 1964	declares the caesium 133 hyperfine transition to be the recommended standard
	12th CGPM, 1964	empowers the CIPM to investigate atomic and molecular frequency standards
	13th CGPM, 1967/68	defines the second in terms of the caesium transition
	CCDS, 1970	defines International Atomic Time, TAI
	14th CGPM, 1971	requests the CIPM to define and establish International Atomic Time, TAI
	15th CGPM, 1975	endorses the use of Coordinated Universal Time, UTC

Electrical units

	CIPM, 1946	definition of mechanical and electrical units in the SI
	14th CGPM, 1971	adopts the name siemens, synmbol S, for electrical conductance
	18th CGPM, 1987	forthcoming adjustment to the representation of the volt and of the ohm
	CIPM, 1988	Josephson effect
	CIPM, 1988	quantum Hall effect
	CIPM, 2000	realization of the ohm using the value of the von Klitzing constant

Thermodynamic temperature

	9th CGPM, 1948	adopts the triple point of water as the thermodynamic reference point, adopts the zero of Celsius temperature to be 0.01 degree below the triple point
	CIPM, 1948	adopts the name degree Celsius for the Celsius temperature scale
	10th CGPM, 1954	defines thermodynamic temperature such that the triple point of water is 273.16 degrees Kelvin exactly, defines standard atmosphere
	13th CGPM, 1967/68	decides formal definition of the kelvin, symbol K
	CIPM, 1989	the International Temperature Scale of 1990, ITS-90
	CIPM, 2005	note added to the definition of the kelvin concerning the isotopic composition of water

Amount of substance

	14th CGPM, 1971	definition of the mole, symbol mol, as a seventh base unit, and roles for its use
	21st CGPM, 1999	adopts the special name katal, kat

Luminous intensity

	CIPM, 1946	definitions of photometric units, new candle and new lumen
	13th CGPM, 1967/68	defines the candela, symbol cd, in terms of a black body
	16th CGPM, 1979	redefines the candela in terms of monochromatic radiation

Note:

For the official text, please refer to the PDF files available at:

http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf (in English) and

http://www.bipm.org/utils/common/pdf/si_brochure_8_fr.pdf (in French).