The previous paragraphs of this chapter give a brief overview of the way in which a system of units, and the International System of Units in particular, is established. This note gives a brief account of the historical development of the International System.
The 9th CGPM (1948, Resolution 6) instructed the CIPM:
to study the establishment of a complete set of rules for units of measurement;
to find out for this purpose, by official enquiry, the opinion prevailing in scientific, technical and educational circles in all countries;
to make recommendations on the establishment of a practical system of units of measurement suitable for adoption by all signatories to the Convention du Mètre.
The same CGPM also laid down, in Resolution 7, general principles for the writing of unit symbols, and listed some coherent derived units which were assigned special names.
The 10th CGPM (1954, Resolution 6) and the 14th CGPM (1971, Resolution 3) adopted as base units of this practical system of units the units of the following seven quantities: length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity.
The 11th CGPM (1960, Resolution 12) adopted the name Système International d'Unités, with the international abbreviation SI, for this practical system of units and laid down rules for prefixes, derived units, and the former supplementary units, and other matters; it thus established a comprehensive specification for units of measurement. Subsequent meetings of the CGPM and CIPM have added to, and modified as necessary, the original structure of the SI to take account of advances in science and of the needs of users.
The historical sequence that led to these important CGPM decisions is summarized here.