Conference Generale des Poids et Mesures

The Conférence Générale des Poids et Mesures (General Conference on Weights and Measures or CGPM) is one of the three organizations established to maintain the SI system under the terms of the Metre Convention (1875). It meets in Paris every four to six years. In 2002 the CGPM represented 51 member states and ten further associate members. [1]

CGPM Meetings

• 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, Sèvres, France. International prototype metre sanctioned.
• 2nd (1897)
• 3rd (1901) - use of kilogram for force or weight prohibited. Litre redefined as volume of 1 kg of water.
• 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.
• 8th (1933) - need for absolute electrical unit identified.
• 9th (1948) - ampere defined. Lowercase l adopted as symbol for litre.
• 10th (1954) - kelvin defined. International System of Units (metre, kilogram, second, ampere, Kelvin, candela) began.
• 11th (1960) - metre redefined in terms of wavelengths of light. Hertz adopted. New metric system given the official symbol SI for Système International d'Unités, the "modernized metric system".
• 12th (1964) - original definition of litre = 1 dm³ restored.
• 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 cesium-133 atom. Degree Kelvin renamed kelvin. Candela redefined.
• 14th (1971) - mole defined. Pascal, newton per square metre, siemens approved.
• 15th (1975) - peta- and exa- prefixes. Gray and becquerel radiological units.
• 16th (1979) - candela defined. Both l and L provisioanlly 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, K_J, and von Klitzing constant, R_K.
• 19th (1991) - new prefixes zetta-, yotta- and yocto-.
• 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) - forthcoming

References [1] http://www.bipm.fr/enus/1_Convention/member_states