Guide for the Use of the International System of Units (SI)

C.2 United States version of defining document for the SI: NIST SP 330 
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 [2]; 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 [3], 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. [1] (see Sec. C.1), SP 330 is the authoritative source document on the SI for the purposes of this 
Guide.
C.3 ISO and IEC 
 
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. [1] 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 
[4], which constitute a series of international consensus standards published by ISO. 
IEC 60027-1—IEC 60027-4 [5] 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. [1] 
published by the BIPM (see Sec. C.1), and they are coordinated with the ISO standards [4].