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International Standard ISO 31 (Quantities and units, International Organization for Standardization, 1992) was the most widely respected[weasel words] style guide for the use of physical quantities and units of measurement, and formulas involving them, in scientific and educational documents worldwide. In most countries, the notations used in mathematics and science textbooks at schools and universities follow closely the guidelines given by ISO 31. It is now superseded by the harmonized ISO/IEC 80000 standard.
The standard comes in 14 parts:
- ISO 31-0: General principles
- ISO 31-1: Space and time (replaced by ISO/IEC 80000-3:2007)
- ISO 31-2: Periodic and related phenomena (replaced by ISO/IEC 80000-3:2007)
- ISO 31-3: Mechanics (replaced by ISO/IEC 80000-4:2006)
- ISO 31-4: Heat (replaced by ISO/IEC 80000-5:2007)
- ISO 31-5: Electricity and magnetism
- ISO 31-6: Light and related electromagnetic radiations
- ISO 31-7: Acoustics (replaced by ISO/IEC 80000-8:2007)
- ISO 31-8: Physical chemistry and molecular physics
- ISO 31-9: Atomic and nuclear physics
- ISO 31-10: Nuclear reactions and ionizing radiations
- ISO 31-11: Mathematical signs and symbols for use in the physical sciences and technology (replaced by ISO 80000-2:2009)
- ISO 31-12: Characteristic numbers
- ISO 31-13: Solid state physics
A second international standard on quantities and units was IEC 60027. The ISO 31 and IEC 60027 Standards were revised by the two standardization organizations in collaboration (, ) to integrate both standards into a joint standard ISO/IEC 80000 - Quantities and Units in which the quantities and equations used with SI are to be referred as the International System of Quantities (ISQ). ISO/IEC 80000 supersedes both ISO 31 and part of IEC 60027.
ISO 31-0 introduced several new words into the English language that are direct spelling-calques from the French. The intention was that these words be used in scientific papers for the sake of convenience and clarity.
|New phrase||Existing phrase||Technical meaning|
|massic <quantity>||specific <quantity>||a quantity divided by its associated mass|
|volumic <quantity>||[volumic] <quantity> density||a quantity divided by its associated volume|
|areic <quantity>||surface <quantity> density||a quantity divided by its associated area|
|lineic <quantity>||linear <quantity> density||a quantity divided by its associated length|
Related national standards
- Canada: CAN/CSA-Z234-1-89 Canadian Metric Practice Guide (covers some aspects of ISO 31-0, but is not a comprehensive list of physical quantities comparable to ISO 31)
- United States: There are several national SI guidance documents, such as NIST SP 811, NIST SP 330, NIST SP 814, IEEE/ASTM SI 10, SAE J916. These cover many aspects of the ISO 31-0 standard, but lack the comprehensive list of quantities and units defined in the remaining parts of ISO 31.
- SI – the international system of units
- BIPM – publishes freely available information on SI units , which overlaps with some of the material covered in ISO 31-0
- IUPAP – much of the material in ISO 31 comes originally from Document IUPAP-25 of the Commission for Symbols, Units and Nomenclature (SUN Commission)  of the International Union of Pure and Applied Physics
- IUPAC – some of the material in ISO 31 originates from the Interdivisional Committee on Terminology, Nomenclature and Symbols  of the International Union of Pure and Applied Chemistry
- Quantities, Units and Symbols in Physical Chemistry – this IUPAC "Green Book" covers many ISO 31 definitions
- IEC 60027 Letter symbols to be used in electrical technology
- ISO 1000 SI Units and Recommendations for the use of their multiples and of certain other units (bundled with ISO 31 as the ISO Standards Handbook – Quantities and units)
- NIST SP811(§8.9)
- International Organization for Standardization (1993). ISO Standards Handbook: Quantities and units (3rd edition). Geneva: ISO. ISBN 92-67-10185-4. (contains both ISO 31 and ISO 1000)
- Cohen, E. R.; Giacomo, P. (1987). "Symbols, Units, Nomenclature and Fundamental Constants in Physics (1987 Revision), Document IUPAP-25 (IUPAP–SUNAMCO 87–1)". Physica A 146: 1–68. Bibcode:1987PhyA..146D...9C. doi:10.1016/0378-4371(87)90215-9.
- ISO TC12 standards – Quantities, units, symbols, conversion factors