The Metre Convention was signed on the 20 May 1875 by 17 Member States. This diplomatic convention was aimed at the promotion of the metric system, and the creation of a scientific bureau, the International Bureau of Weights and Measures (BIPM). The number of Member States stands currently at 51, of which 24 European countries.
It must be noted that the president of the International Committee of Weights and Measures (CIPM), the vice-president, the secretary and the director of the CIPM should be of different nationalities. It is the desire to endeavour in common to make progress in science that has led the Member States to join the Metre Convention; through their membership, they not only consider their own interest but they also recognise therein the necessity for all the countries to participate in a world progress work that will also benefit them.
The CGPM meets at least once every six years upon notification by the French Ministry of Foreign Affairs. Currently and since 1960, the CGPM meetings are held every four years. This is a diplomatic conference that brings together the delegates from the Member States of the Metre Convention.
The opening session is chaired by the French Minister of Foreign Affairs and the working sessions by the Président de l'Académie des Sciences de Paris.
The CGPM’s missions :
The CIPM meets once a year. It comprises eighteen personalities, eminent scientists and metrologists with different nationalities, and elected in a personal capacity by the CGPM. France has always been represented at the CIPM.
The CIPM’s missions :
Owing to the ever increasing number of new Member States and the consequential new scientific and technical works developed by the NMIs, the CIPM has created, since 1927, a series of Consultative Committees (CCs) to allow studying thoroughly the scientific and technical progress that could have a high influence on metrology.
The Consultative Committees are made up of world experts and specialists working in the NMIs. Since the CCs have restricted membership, all the members of the Metre Convention are therefore not represented in each of the CCs. The CCs must be chaired by one CIPM member.
The CCs’ missions:
Until to date ten CCs have been created :
The BIPM, located in the "Pavillon de Breteuil" in Sèvres, is a scientific metrology laboratory which primary mission is to ensure the uniformity of the measurements (either physical or chemical) across the world.
The Director of the BIPM is appointed by the CGPM.
The BIPM carries out fundamental research aimed at the improvement of the reference standards in collaboration with the National Metrology Institutes (NMIs), participates in and organises the international comparisons, maintains the reference standards for which it is responsible.
The only quantity that is currently represented by one material standard is the mass. The must maintain the international prototype of the kilogram, the K, to which the NMIs must compare themselves. Said comparison is very rarely carried out so as to avoid altering the characteristics of the international prototype. And just three comparisons have been made up to date.
The BIPM operates thanks to the contributions paid by each Member State that has joined the Metre Convention. The annual dotation allocated to the BIPM, and defined during the CGPM, is distributed over the States according to a scale based on the United Nations Organization coefficient, but within maximum limits of 10 % and minimum limits of 0,5 % of total dotation.
All the States that contribute to maintaining the BIPM are co-owners of its facilities.