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. 
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.
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