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This is the sixth edition of CSA Standard Z234.1, Metric Practice Guide. It supersedes previous editions published, under the title Canadian Metric Practice Guide, in 1989, 1979, 1976, 1973, and 1970.
This Standard is intended to be a primary source of knowledge for the application of the SI for all purposes and to provide a basis for its specific application in individual fields of interest.
The CSA Technical Committee on Metric Practice was established in 1967 to prepare Standards of a general nature on the metric system. It was realized that, as a first step, a set of authoritative conversion factors would have to be issued relating Canadian units of measure to those of the International System of Units, an aim achieved in 1970 with the publication of the first edition of CSA Standard Z234.1. A second edition was published in 1973, the scope now broadened to include information dealing with the application of the SI. The third edition, published in 1976, introduced two new prefixes, two new SI units, and an appendix on recommended spellings. The fourth edition added more new material, provided greater guidance in conversion and rounding, and rearranged the contents to facilitate the use of the Guide. A fifth edition, published in 1989, incorporated decisions made by the General Conference on Weights and Measures (CGPM) since 1979, particularly concerning the definition of the metre and the symbol for the litre.
The sixth edition of the Standard includes a number of important CGPM and International Committee for Weights and Measures (CIPM) decisions. In particular, it includes four new prefixes and recognizes the elimination of the category of supplementary units. It also attempts to harmonize with the ISO 31 series of standards for definitions of quantities and units, which has resulted in a redefinition of logarithmic quantities. The new edition also reflects the changes that are being proposed by ISO, specifically the distinction between prefixes for binary and decimal multiples.
The structure of the Standard has been changed considerably. For example, some information dealing with conversions has been reworded and placed in an Appendix, in recognition of the fact that conversion from older systems of measurement to the SI is now largely complete. An Appendix on equations and coherence has been added to clarify the meaning of these terms in the SI. Ready access to technical information on the Internet has provided for an Appendix that lists some of the more important Web sites. Many other changes have been made to this sixth edition, mainly to increase the Standard’s ease of use and to make it particularly user-friendly.
This Standard was prepared by the CSA Technical Committee on International System of Units (SI) under the jurisdiction of the Standards Steering Committee on Basic Engineering Standards, and has been formally approved by the Technical Committee. It will be submitted to the Standards Council of Canada for approval as a National Standard of Canada.
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.
In this Standard, shall indicates a 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.