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Notice

Interpretation of the International System of Units (the Metric System of Measurement) for the United States

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Information about this document as published in the Federal Register.

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AGENCY:

National Institute of Standards and Technology, Commerce.

ACTION:

Notice.

SUMMARY:

The International System of Units (SI) (the metric system of measurement) has been recognized for use in the United States since 1866 (15 U.S.C. 204) and is the preferred system of measurement for trade and commerce. The SI was established and is maintained by the General Conference of Weights and Measures and is interpreted or modified for use in the United States by the National Institute of Standards and Technology (NIST) by authority of the Secretary of Commerce (15 U.S.C. 205). This notice describes the recent modifications to the SI and announces the publication of the latest interpretation of the SI for the United States in the 2008 Edition of NIST Special Publication 330 “The International System of Units.” The 2008 Edition of NIST Special Publication 811 “Guide for the Use of the International System of Units” was also published. Together these publications provide the legal interpretation of and guidelines for the use of the SI in the United States.

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FOR FURTHER INFORMATION CONTACT:

Dr. Ambler Thompson, National Institute of Standards and Technology, Weights and Measures Division, International Legal Metrology Group, 100 Bureau Drive, Stop 2600, Gaithersburg, MD 20899-2600 or by telephone (301) 975-2333, Fax: (301) 975-8091, or by e-mail at ambler.thompson@nist.gov.

For information regarding NIST's efforts to coordinate the transition to the International System of Units, contact: Elizabeth Gentry, Metric Coordinator, National Institute of Standards and Technology, Weights and Measures Division, Laws and Metric Group, 100 Bureau Drive, Stop 2600, Gaithersburg, MD 20899-2600 or by telephone (301) 975-3690, Fax (301) 975-8091, or by e-mail at TheSI@nist.gov.

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SUPPLEMENTARY INFORMATION:

The International System of Units (abbreviated as SI in all languages), generally known as the metric system, is the preferred system of measurement for use in trade and commerce in the United States (15 U.S.C. 205b) but use of traditional systems of weights and measures in non-business activities is permitted. The SI was established in 1960 by the General Conference of Weights and Measures (abbreviated CGPM in all languages) and is interpreted, or modified for, the United States by the Secretary of Commerce (15 U.S.C. 205c) who has delegated this authority to the Director of the National Institute of Standards and Technology (NIST). The CGPM is an international organization established by the Meter Convention in 1875 in which more than 50 countries participate. One of the responsibilities of the CGPM is to ensure the SI reflects the latest advances in science and technology and provides a single international language for measurement. In 2006 the CGPM published changes to the SI in the 8th Edition of the Bureau of International Weights and Measures SI publication commonly known as the “SI Brochure.” This notice describes the modifications to the SI and announces the publication of the latest interpretation of the SI for the United States in the 2008 Edition of NIST Special Publication (SP) 330 “The International System of Units (SI).”

NIST SP 330 describes the history of the Meter Convention, explains how the International System of Units was developed, and describes the global effort to maintain the system. A comprehensive description of the SI's base units, terminology, units and symbols is also provided. A description of the decimal system and the appropriate multiples and submultiples to be used in expressing units and values is included. Also provided are editorial style guidelines to ensure that SI values and units are properly formatted and clearly written. NIST has also published the 2008 Edition of its Special Publication 811 “Guide for the Use of the International System of Units (SI),” which includes additional guidance on the use of the SI and a broad range of conversion factors. When used together, these publications provide the most current interpretation of the SI and present the latest guidance on the use of the SI in the United States.

I. Changes to the International System of Units (SI)

The CGPM adopted the following changes in the 8th Edition (2006) of the SI Brochure and these have been Start Printed Page 28433incorporated in the 2008 Edition of NIST SP 330:

a. Full incorporation of the 2000 Supplement which clarified the definition of the second and incorporated the new coherent SI unit with a special name and symbol for the mol s−1, the katal with symbol kat, for expressing values of the quantity catalytic activity;

b. A discussion designated as “the set of coherent SI units” was added to clarify that the base and coherent derived units of the SI form a coherent set;

c. New section entitled “Units for quantities that describe biological effects” was added in view of their importance for human health and safety;

d. New section entitled “Historical note” was added to provide updated information from Section 1.1 of the 7th Edition;

e. Appendix 1 was updated to include all the recent decisions of the CIPM and CGPM which impact the SI;

f. Appendix 2, which discusses the experimental realization of units, is made available only in electronic form on the BIPM Web site at http://www.bipm.org/​en/​si/​si_​brochure/​appendix2/​, so that it may be easily updated between SI brochure versions; and

g. New Appendix 3 entitled “Units for photochemical and photobiological quantities,” was added to point out that the SI already includes a SI base unit, the candela, which is considered to be a biological effects unit of importance to industry and human health and safety.

II. Modifications to the SI for Its Use in the United States

The 2008 Edition of NIST SP 330 differs from the “SI Brochure” to conform to the language and customary use of measurement units in the United States:

a. The spelling of English words 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. Thus, the spellings “meter,” “liter,” and “deca” are used rather than “metre,” “litre,” and “deka” as in the original BIPM English text;

b. The name of the unit with symbol t is defined according to 1 t = 103 kg which is called “metric ton” rather than “tonne;”

c. The four units curie, roentgen, rad, and rem are included in Table 10;

d. A number of Editors' notes are added in order to indicate differences of interpretation and to clarify the text;

e. A few minor editorial changes are made in order to “Americanize” some phrases.

This notice supersedes the last interpretation of the SI that was published in the Federal Register on July 28, 1998 (Vol. 63, No. 144—FR 40334—40340).

NIST SP 330, NIST SP 811, and other useful information regarding the International System of Units (SI) are published electronically (http://physics.nist.gov/​cuu/​Units/​index.html and http://nist.gov/​metric) and in hard copy. Requests for hardcopies can be sent to: TheSI@nist.gov.

Although there is no formal comment period, comments and suggestions on the SI are invited and should be sent to Dr. Ambler Thompson at the address previously indicated.

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Dated: May 9, 2008.

James M.Turner,

Deputy Director.

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[FR Doc. E8-11058 Filed 5-15-08; 8:45 am]

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