This document@ which supersedes IEEE/ASTM SI 10-1997@ is the primary American National Standard for use of the International System of Units (SI). The first version of this standard was published by IEEE and ASTM in 1976. The sponsoring societies welcome comments and suggestions from interested individuals and organizations.In 1988 the Metric Conversion Act was amended to designate ??the metric system of measurement as the preferred system of weights and measures for United States trade and commerce.?? With the increasing importance of the global marketplace@ it has become imperative for U.S. industry to extend its use of SI and for U.S. citizens to gain a working knowledge of this modern metric system. This standard is intended to give authoritative information on SI and appropriate guidance concerning its application.SI is defined in the document Le Syst??me International d??Unit??s@ published in French@ with an English translation@ by the International Bureau of Weights and Measures (BIPM). The BIPM was set up by the Convention du M??tre@ signed in 1875 (see Annex D). Le Syst??me International d??Unit??s@ known informally as the ??BIPM SI brochure@?? is revised from time to time in accordance with the decisions of the General Conference on Weights and Measures (CGPM) and other international organizations. A U.S. version is published by NIST [B26].IEEE/ASTM SI 10-2002 is consistent with the SI brochure in all matters that concern the SI itself@ except that it presents the degree Celsius as simply another name for the kelvin that is used to express Celsius temperature@ while the BIPM SI Brochure lists the degree Celsius as an SI derived unit. Of more practical importance is the difference in approach to non-SI units. IEEE/ASTM SI 10 and its predecessors have traditionally been more restrictive in their recommendations concerning the use of non-SI units. The SI Brochure@ for example@ lists the ?ngstr?m as a unit that is ??currently accepted for use with the International System@?? and lists the cgs units and many others as units whose use ??is not encouraged.?? IEEE/ASTM SI 10@ intended for the United States and developed under the consensus standardization process@ makes the significantly stronger recommendation that these units are ??not to be used.??Guidance for the use of the modern metric system is given. Known as the International System of Units (abbreviated SI)@ the system is the basis for worldwide standardization of measurement units. Information is included on SI@ a list of units recognized for use with SI@ and a list of conversion factors@ together with general guidance on proper style and usage.The International System of Units is the form of the metric system that is generally in use around the world. This document gives guidance for the use of this system. It is the primary American National Standard for conformity to the International System of Units (or the SI@ as it is abbreviated from its name in French@ Le Syst??me International d??Unit??s).Any measurable quantity can be represented in this system with the aid of just seven ??base?? units@ used directly for the quantities length@ mass@ time@ electric current@ temperature@ amount of substance@ and luminous intensity@ or by combinations (called ??derived?? units) of these seven. For example@ the unit of speed can be expressed by the unit of length divided by the unit of time. The SI is a complete and coherent system.This standard shows first the two classes of units (base and derived) that make up the SI@ together with the symbols by which they are known. Prefixes that allow the formation of decimal multiples and submultiples are explained. Then come notes on the proper use of the SI units and symbols in many applications.In the first Annex are lists of many units from non-SI systems with the appropriate SI units that should be substituted and numerical conversion factors. Other annexes include rules for conversion and rounding@ a discussion of the advantages of SI units with definitions where appropriate@ a history of the development of the system@ and a bibliography of source documents.