The defining document for the International System of Units is the Brochure published by the International Bureau of Weights and Measures (BIPM) in French, followed by an English translation . This document is revised from time to time in accordance with the decisions of the General Conference on Weights and Measures (CGPM) and the International Committee for Weights and Measures (CIPM).
The United States edition of the English translation in the BIPM SI Brochure (see Sec. C.1) is published by the National Institute of Standards and Technology as NIST Special Publication 330 ; it differs from the translation in the BIPM publication in the following details:
the spelling of English-language words - for example, "meter," "liter," and "deka" are used instead of "metre," "litre," and "deca" - is in accordance with the United States Government Printing Office Style Manual , which follows Webster's Third New International Dictionary rather than the Oxford Dictionary used in many English-speaking countries. This spelling also reflects recommended United States practice (see Secs. C.1 and C.5);
editorial notes regarding the use of the SI in the United States are added.
Inasmuch as NIST Special Publication 330 reflects the interpretation of the SI for the United States by the U.S. Secretary of Commerce (see the Preface) while at the same time highly consistent with Ref.  (see Sec. C.1), SP 330 is the authoritative source document on the SI for the purposes of this Guide.
The International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) both publish a series of international consensus standards to promote international uniformity in the practical use of the SI in various fields of science and technology, and in particular to standardize the symbols for various quantities and the units in which the values of these quantities are expressed. These standards are in general compatible with Ref.  published by the BIPM (see Sec. C.1).
Currently ISO 31 is being revised jointly by technical committees ISO TC12 and IEC TC25. The revised standards ISO/IEC 80000-1—ISO/IEC 80000-15, will supersede ISO 31-0:1992—ISO 31-13:1992 , which constitute a series of international consensus standards published by ISO.
IEC 60027-1—IEC 60027-4  constitute a series of international consensus standards published by the IEC to promote international uniformity in the practical use of the SI in electrical technology, and in particular to standardize the symbols for various quantities used in electrotechnology and the units in which the values of these quantities are expressed. These IEC standards are also compatible with Ref.  published by the BIPM (see Sec. C.1), and they are coordinated with the ISO standards .
SI 10-2002 "American National Standard for Use of the International System of Units (SI): The Modern Metric System," Ref. , is the product of a joint effort by Institute of Electrical and Electronics Engineers (IEEE) and ASTM International (ASTM) to develop a single American National Standard Institute (ANSI) standard.26 It is based on the International System of Units as interpreted for use in the United States (see Secs. C.1 and C.2), and has been approved by a consensus of providers and consumers that includes interests in industrial organizations, government agencies, and scientific associations. SI 10 is recommended as a comprehensive source of authoritative information for the practical use of the SI in the United States. (Similar documents have also been developed by other North American technical organizations; see Ref. , note 1.)
Important details concerning United States customary units of measurement and the interpretation of the SI for the United States are published from time to time in the Federal Register; these notices have the status of official United States Government policy.
A Federal Register notice of July 1, 1959  states the values of conversion factors to be used in technical and scientific fields to obtain the values of the United States yard and pound from the SI base units for length and mass, the meter and the kilogram. These conversion factors were adopted on the basis of an agreement of English-speaking countries to reconcile small differences in the values of the inch-pound units as they were used in different parts of the world. This action did not affect the value of the yard or foot used for geodetic surveys in the United States. Thus, at that time, it became necessary to recognize on a temporary basis a small difference between United States customary units of length for "international measure" and "survey measure." A Federal Register notice of July 19, 1988  announced a tentative decision not to adopt the international foot of 0.3048 meters for surveying and mapping activities in the United States. A final decision to continue the use of the survey foot indefinitely is pending the completion of an analysis of public comments on the tentative decision; this decision will also be announced in the Federal Register.
Even if a final decision affirms the continued use of the survey foot in surveying and mapping services of the United States, it is significant to note that the Office of Charting and Geodetic Services of the National Ocean Service in the National Oceanic and Atmospheric Administration uses the meter exclusively for the North American Datum . The North American Datum of 1983, the most recent definition and adjustment of this information, was announced in a Federal Register notice of June 14, 1989 .
The definitions of the international foot and yard and the corresponding survey units are also addressed in a Federal Register Notice published on February 3, 1975 .
A Federal Register notice of July 27, 1968  provides a list of the common customary measurement units used in commerce throughout the United States, together with the conversion factors that link them with the meter and the kilogram.
A recent Federal Register notice concerning the SI  is a restatement of the interpretation of the International System for use in the United States, and it updates the corresponding information published in earlier notices.
A Federal Register notice of January 2, 1991  removes the voluntary aspect of the conversion to the SI for Federal agencies and provides policy direction to assist Federal agencies in their transition to the use of the metric system of measurement.
A Federal Register notice of July 29, 1991  provides Presidential authority and direction for the use of the metric system of measurement by Federal departments and agencies in their programs.
A Federal Register Notice of July 28, 1998,  declares that there are now only two classes of units in the International System of Units: base units and derived units. The units of these two classes form a coherent set of units and are designated by the name "SI units."
Federal Standard 376B  was developed by the Standards and Metric Practices Subcommittee of the Metrication Operating Committee, which operates under the Interagency Council on Metric Policy. Specified in the Federal Standardization Handbook and issued by, and available from, the General Services Administration, Washington, DC, 20406, it is the basic Federal standard that lists preferred metric units for use throughout the Federal Government. It gives guidance on the selection of metric units required to comply with PL 94-168 (see Preface) as amended by PL 100-418 (see Preface), and with Executive Order 12770  (see Sec. C.5).
The set of self-consistent recommended values of the fundamental physical constants resulting from the 2006 Committee on Data for Science and Technology (CODATA) least-squares adjustment of the constants  can be found at the NIST website: http://physics.nist.gov/cuu/Constants/index.html. The definitive paper describing the 2006 adjustment has been accepted for publication and a preprint is available at http://physics.nist.gov/cuu/Constants/codata.pdf.
Reference  cites two publications that describe the evaluation and expression of uncertainty in measurement based on the approach recommended by the CIPM in 1981 and which have been adopted worldwide.