Metric Practice Guide
This Standard is a guide for the understanding and application of the International System of Units ("Système international d'unités"), for which the universal abbreviation is SI. Information is included on quantities, SI units, and the recommended application of SI multiples and submultiples. Up-to-date terminology for quantities and conversion factors that relate the SI to other
systems of units is also provided. The conversion and rounding of data and dual dimensioning are also addressed.
Note: See Appendix B for a summary of basic SI rules.
In this Standard, "shall" indicates a mandatory requirement; "should" indicates a recommendation or that which is advised but not mandatory; and "may" indicates an advisory or optional statement. Notes accompanying clauses do not include mandatory or alternative requirements. The purpose of a note accompanying a clause is to separate from the text explanatory or informative material that is not properly a part of the requirements of this Standard.
Notes to tables and figures are considered part of the table or figure and may be written as mandatory requirements. Legends to equations and figures are
considered to be mandatory requirements.
In particular, "shall" is used whenever there is only one way to comply with the SI standard. "Should" is used when there are options within the SI, but Si has established a preference. "May" is used when there are options within the
SI and the SI has no preference.