<P> The International System of Quantities (ISQ) is a system based on seven base quantities: length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity . Other quantities such as area, pressure, and electrical resistance are derived from these base quantities by clear non-contradictory equations . The ISQ defines the quantities that are measured with the SI units . The ISQ is defined in the international standard ISO / IEC 80000, and was finalised in 2009 with the publication of ISO 80000 - 1 . </P> <P> The CGPM publishes a brochure which defines and presents SI . Its official version is in French, in line with the Metre Convention . It leaves some scope for local interpretation, particularly regarding names and terms in different languages, so for example the United States' National Institute of Standards and Technology (NIST) has produced a version of the CGPM document (NIST SP 330) which clarifies local interpretation for English - language publications that use American English and another document (NIST SP 811) that gives general guidance for the use of SI in the United States and conversion factors between SI and customary units . </P> <P> The writing and maintenance of the CGPM brochure is carried out by one of the committees of the International Committee for Weights and Measures (CIPM), the Consultative Committee for Units (CCU). The CIPM nominates the chairman of this committee, but the committee includes representatives of various other international bodies rather than CIPM or CGPM nominees . This committee thus provides a forum for the bodies concerned to provide input to the CIPM in respect of ongoing enhancements to SI . </P> <P> The definitions of the terms "quantity", "unit", "dimension" etc. that are used in the SI Brochure are those given in the International vocabulary of metrology, a publication produced by the Joint Committee for Guides in Metrology (JCGM), a working group consisting of eight international standards organisations under the chairmanship of the director of the BIPM . The quantities and equations that define the SI units are now referred to as the International System of Quantities (ISQ), and are set out in the International Standard ISO / IEC 80000 Quantities and Units . </P>

In a system of measurement all units are derived from a base unit