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

1.2 Outline of Guide 
The Preface gives the principal Federal Government actions taken since 1988 regarding the SI and 
introduces the international body— the CGPM—that is responsible for the SI.
A check list immediately follows the Preface to help NIST authors review the conformity of their 
manuscripts with proper SI usage and the basic principles concerning quantities and units.
A detailed Contents, the aim of which is to simplify the use of the Guide, follows the check list. 
This introductory chapter gives the purpose of the Guide and its outline, while Chapter 2 summarizes 
and clarifies the NIST policy on the use of the SI in NIST publications. 
Chapter 3 notes the existence of a number of publications on the SI and gives the two organizational 
units at NIST to which questions concerning the SI may be directed and from which additional information 
about the SI may be obtained. 
Chapter 4 discusses the fundamental aspects of the SI, including the two current classes of SI units: 
base, and derived; those derived units that have special names and symbols, including the degree Celsius; 
and the SI prefixes that are used to form decimal multiples and submultiples of units. 
Chapter 5 discusses units that are outside the SI and indicates those that may be used with it and 
those that may not. It also gives (see Sec. 5.4) precise definitions of the terms “SI units” and “acceptable 
units” as used in this Guide. 
Chapter 6 gives the rules and style conventions for printing and using units, especially unit symbols 
and SI prefix symbols.
Chapters 7 and 8, which some readers may view as the most important parts of this Guide, provide, 
respectively, the rules and style conventions for expressing the values of quantities, and clarifying 
comments on some often troublesome quantities and their units.
Chapter 9 gives the rules and style conventions for spelling unit names.
Chapter 10 further elaborates on printing and using symbols and numbers in scientific and technical 
documents and is intended to assist NIST authors prepare manuscripts that are consistent with accepted 
typesetting practice. 
Appendix A gives the definitions of the SI base units, while Appendix B gives conversion factors for 
converting values of quantities expressed in units that are mainly unacceptable for use with the SI to values 
expressed mainly in SI units. Appendix B also includes a simplified discussion of rounding numbers and 
rounding converted numerical values of quantities. Appendix C discusses in some detail most of the 
references included in Appendix D—Bibliography, which concludes the Guide.

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