# International sizing system

The International System Size abbreviated, ISQ (of English International System of Quantities ) is a sizing system , which the International System of Units (SI) is used. This size system has been published in the multi-part international series of standards ISO and IEC 80000.

## International Size System (ISQ)

In order to be able to use a system of units such as the SI, a corresponding size system is required. In particular, a set of equations is needed to define the relationships between the quantities , since these equations also define the relationships between the units. For the definition of the units in the SI, a limited selection of units was chosen as base units , so that all other units are used as derived units , i.e. H. can be expressed as products of powers of the base units. In the same way, the corresponding quantities are described in the ISQ as base quantities and derived quantities . Each base quantity is assigned a dimension with the same name.

Base units and sizes
Base unit in the SI Base size in the ISQ dimension
Surname character Surname character character
second s time ${\ displaystyle t}$ ${\ displaystyle {\ mathsf {T}}}$
meter m length ${\ displaystyle l}$ ${\ displaystyle {\ mathsf {L}}}$
kilogram kg Dimensions ${\ displaystyle m}$ ${\ displaystyle {\ mathsf {M}}}$
amp A. Amperage ${\ displaystyle I}$ ${\ displaystyle {\ mathsf {I}}}$
Kelvin K thermodynamic temperature ${\ displaystyle T}$ ${\ displaystyle {\ mathsf {\ Theta}}}$
Mole mol Amount of substance ${\ displaystyle n}$ ${\ displaystyle {\ mathsf {N}}}$
Candela CD Light intensity ${\ displaystyle I _ {\ mathrm {v}}}$ ${\ displaystyle {\ mathsf {J}}}$

The equations that reduce the derived quantities to basic quantities can also be used to express the derived units in terms of the basic units. In general, it is therefore advisable to first determine the quantities and the equations that link the quantities with one another and then to select the appropriate units.

Most of the units were developed before the concept of the size system was defined. The size system to be used with the SI is given by the sizes and equations used in scientific publications and manuals. However, such sources only contain a small selection of the innumerable possible quantities and equations. A large number of quantities and equations have been compiled in the international standards ISO 31 and IEC 60027. The content of these standards was later harmonized by ISO and IEC and published as the international standard ISO / IEC 80000 sizes and units from 2006 .

In EN ISO 80000, the size system used with the SI is called the "International Size System". The corresponding abbreviation "ISQ" (from the English International System of Quantities ) should apply in all languages.

## ISO 80000 and IEC 80000

The ISO or IEC 80000 sizes and units was published in two language versions of equal rank in English (Quantities and units) and French (Grandeurs et unités) . This international standard has been incorporated into various national standards and translated into the corresponding languages ​​for this purpose. The various parts were adopted by the European Committee for Standardization (CEN) as EN ISO 80000 or EN 80000 for the corresponding parts of the European standard without any changes to the content . The German versions were published as DIN EN ISO 80000 and DIN EN 80000. Versions in German have also been published in Austria as ÖNORM EN ISO 80000 or ÖVE / ÖNORM EN 80000 or are available as drafts.

The ISO or IEC 80000 consists of 14 individually available parts, each published by the ISO (11 parts) or the IEC (3 parts). The Technical Committee responsible for developing the standards ( English Technical Committee , abbreviated to TC ) is TC 12 (Quantities, units, symbols, conversion factors) at ISO and TC 25 (Quantities and units, and their letter symbols ) at IEC ) . The first valid editions of the individual parts appeared in the period from 2006 to 2009. They replace the ISO 31 and ISO 1000 standards that have been repealed . The following table gives an overview of the individual parts:

Parts of ISO and IEC 80000
Output as First edition of as DIN EN currently from Original title Title of the German version
English French
ISO 80000-1 Nov 2009 Aug 2013 general Généralités General
ISO 80000-2 Dec 2009 Feb 2020 Mathematics Mathématiques mathematics
ISO 80000-3 March 2006 Aug 2013 Space and time Espace et temps space and time
ISO 80000-4 March 2006 Jan. 2020 Mechanics Mecanique mechanics
ISO 80000-5 May 2007 Feb 2020 Thermodynamics Thermodynamique thermodynamics
IEC 80000‑6 March 2008 Sep 2008 Electromagnetism Electromagnétisme Electromagnetism
ISO 80000-7 Nov 2008 Takeover has ceased at CEN Light Lumière light
ISO 80000-8 June 2007 June 2020 Acoustics Acoustique Acoustics
ISO 80000-9 April 2009 Feb 2020 Physical chemistry and molecular physics Chimie physique et physique moléculaire Physical chemistry and molecular physics
ISO 80000-10 Dec 2009 Feb 2020 Atomic and nuclear physics Physique atomique et nucléaire Atomic and Nuclear Physics
ISO 80000-11 Dec 2008 Aug 2013 Characteristic numbers Nombres caractéristiques Characteristics of the dimension number
ISO 80000-12 May 2009 Feb 2020 Condensed matter physics Physique de la matière condensée Condensed Matter Physics
IEC 80000-13 March 2008 Jan. 2009 Information science and technology Science et technologies de l'information Information science and technology
IEC 80000-14 March 2008 Aug 2009 Telebiometrics related to human physiology Télébiométrique relative à la physiologie humaine Telebiometric identification in the conditions of human physiology

Part 1 General applies to general use within the various fields of science and technology. It contains general information and definitions regarding sizes (especially the ISQ) and units (especially the SI) as well as extensive writing rules. It also serves as an introduction to the other parts of ISO and IEC 80000.

Part 2 Mathematics contains general information on mathematical symbols, their meaning, way of speaking and application.

The remaining parts contain terms, symbols and definitions for quantities and units for each scientific topic.

The number of quantities used in the scientific field is unlimited, so it is not possible to compile a complete list of quantities and derived units. It is therefore inevitable that some users working in particular specialist areas will want to use sizes that are not listed in ISO or IEC 80000 or in any other international standard. However, this is not an obstacle to the definition of units for own quantities, provided that these quantities can be related to similar examples listed.

## Individual evidence

1. ISO 80000-1: 2009, Quantities and units - Part 1: General , November 15, 2009. Corrected by: ISO 80000-1: 2009 / Cor.1: 2011, Technical Corrigendum 1 to ISO 80000- 1: 2009 , October 1, 2011.
2. JCGM 200: 2012 International vocabulary of metrology - Basic and general concepts and associated terms (VIM) , 3rd edition, 2012.
3. a b c d Bureau international des poids et mesures (BIPM) : Le Système international d'unités (SI) , 9e édition 2019, engl. and franz.
4. ISO / TC 12 website
5. IEC / TC 25 website