On May 20, 1875, seventeen states signed an international treaty known as the Convention du Mètre (Meter Convention). This treaty established an international organization, the Bureau International des Pois et Mesueres (International Bureau of Weights and Measures, BIPM), which is made up of:
- General Conference on Weights and Measures (Conférence générale des poids et mesures, GFCM), an intergovernmental conference of official delegates from member countries and the supreme authority for all actions;
- International Committee for Weights and Measures (Comité international des poids et mesures, CIPM), composed of selected scientists and metrologists, which prepares and executes the decisions of the CGPM and is responsible for the supervision of the International Bureau of Weights and Measures;
- A laboratory and permanent secretariat, whose activities include the establishment of the basic standards and scales of the main physical quantities and the maintenance of prototype international standards.
The goal is to act together on matters related to measurement science and measurement standards.
The CGPM Meets in Paris, generally every four years, and is chaired by the President of the Paris Academy of Sciences.
Throughout its history, the most important meetings were:
1889 - The meter was defined as the distance between two lines on a bar made of an alloy of platinum with 10% iridium, measured at the melting point of ice.
1901 – The liter was redefined as the volume of 1 kg of water. Clarified that kilograms are units of mass
1913 – The International Temperature Scale was proposed
1948 – Ampere, bar, coulomb, farad, henry, joule, newton, ohm, volt, watt, weber were defined. The degree Celsius was selected from three names in use as the name for the unit of temperature. “l” was adopted as the symbol for the liter. The “,” is adopted as decimal marker symbols.
1960 – Hertz, lumen, lux testa units were adopted. It was indicated to the International System that the official symbol was SI and the prefixes pico-, nano-, micro, mega-, giga- and tera- were confirmed.
1967 - The second was redefined as the 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 at a temperature of 0 K. The degree Kelvin was renamed kelvin and the candle was redefined.
1971 – The mole was adopted as a new SI unit. The names pascal and siemens were approved as units of electrical pressure and conductance.
1975 – The prefixes peta- and exa- are adopted. The gray and becquerel units are adopted as radiological units within the SI.
1979 - The candela and the sievert were defined.
2018 – The kilogram, ampere, kelvin, and mole were redefined, in terms of new permanently fixed values of Planck's constant, elementary charge, Boltzmann's constant, and Avogadro's constant, respectively
If you want to know more, click on the following link: International Bureau of Weights and Measures