SI Brochure and Conversion Factors
The CGPM have published a brochure, the 8th edition of which appeared in 2006, in which the various recommendations that make up SI have been codified. This brochure leaves some scope for local interpretation, particularly in respect of language. The United States National Institute of Standards and Technology has produced a version of the CGPM document (NIST SP 330) which clarifies local interpretation in respect of 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.
The writing and maintenance of the CGPM brochure is carried out by one of the consultative 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 its membership is made up of representatives of various other international bodies rather than CIPM or CGPM nominees. This committee also provides a forum for the bodies concerned to provide input to the CIPM in respect of on-going enhancements to SI. In 2010 the CCU proposed a number of changes to the definitions of the base units used in SI. The CIPM meeting of October 2010 found that the proposal was not complete, and it is expected that the CGPM will consider the full proposal in 2014.
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 ISO/IEC 80000 Quantities and Units.
Appendix B of NIST SP 811, a list of conversion factor between SI and customary units, is an extension to the SI Brochure.
Read more about this topic: International System Of Units
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