- 1st ( 1889 ) - Kilogram defined as mass of the international prototype kilogram (IPK) made of Platinum - Iridium and kept at the International Bureau Of Weights And Measures (Bureau international des poids et mesures), Sèvres , France. International prototype metre sanctioned.
- 2nd ( 1897 )
- 3rd ( 1901 ) - Litre redefined as volume of 1 kg of water. Clarified that kilograms are units of mass, "standard weight" defined, Standard Acceleration Of Gravity defined endorsing use of grams force and making them well-defined.
- 4th ( 1907 ) - Carat = 200 mg adopted.
- 5th ( 1913 ) - International Temperature Scale proposed.
- 6th ( 1921 ) - Metre Convention revised.
- 7th ( 1927 ) - Consultative Committee for Electricity (CCE) created.
- 8 th ( 1933 ) - need for absolute electrical unit identified.
- 9th ( 1948 ) - Ampere , Coulomb , Farad , Henry , Joule , Newton , Ohm , Volt , Watt , Weber defined. Chose Degree Celsius from among the three names then in use. Lowercase l adopted as symbol for litre. Both the comma and dot on a line are accepted as decimal marker symbols. Symbols for the Stere and Second changed {Link without Title} .
- 10th ( 1954 ) - Kelvin , Standard Atmosphere defined. ''International System of Units'' ( Metre , Kilogram , Second , Ampere , Kelvin , Candela ) began.
- 11th ( 1960 ) - metre redefined in terms of wavelengths of light. Hertz , Lumen , Lux , Tesla adopted. New metric system given the official symbol for ''''' Système International D'Unités ''''', the "modernized metric system". Prefixes ''pico-'', ''nano-'', ''micro-'', ''mega-'', ''giga-'' and ''tera-'' confirmed.
- 12 th ( 1964 ) - original definition of Litre = 1 dm³ restored. ''atto-'' and ''femto-'' prefixes.
- 13th ( 1967 ) - second redefined as duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the Caesium -133 atom at a temperature of 0 K. ''Degree Kelvin'' renamed ''kelvin''. Candela redefined.
- 14th ( 1971 ) - new SI Base Unit Mole defined. Pascal , Siemens approved.
- 15th ( 1975 ) - ''peta-'' and ''exa-'' prefixes. Gray and Becquerel radiological units.
- 16th ( 1979 ) - Candela , Sievert defined. Both l and L provisionally allowed as symbols for litre.
- 17th ( 1983 ) - metre redefined in terms of the speed of light, but keeps same length.
- 18th ( 1987 ) - conventional values adopted for Josephson Constant , ''KJ'', and Von Klitzing Constant , ''RK'', preparing the way for alternate definitions of the ampere and kilogram.
- 19th ( 1991 ) - new prefixes '' Yocto -'', '' Zepto -'', '' Zetta -'' and '' Yotta -''.
- 20th ( 1995 ) - supplementary SI units ( Radian and Steradian ) become ''derived units''.
- 21st ( 1999 ) - new SI derived unit, the Katal = Mole per Second , for the expression of catalytic activity.
- 22nd ( 2003 ) - both the comma and dot on a line are reaffirmed as decimal marker symbols {Link without Title} .
(1) CGPM Member States
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