ISO 1 is an
international standard
international standard is a technical standard developed by one or more international standards organizations. International standards are available for consideration and use worldwide. The most prominent such organization is the International Or ...
set by the
International Organization for Standardization
The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Ar ...
that specifies the
standard reference temperature for
geometrical product specification and verification. The temperature is fixed at 20
°C
The degree Celsius is the unit of temperature on the Celsius scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the Kelvin scale. The ...
, which is equal to 293.15
kelvin
The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phys ...
and 68
degrees Fahrenheit
The Fahrenheit scale () is a temperature scale based on one proposed in 1724 by the physicist Daniel Gabriel Fahrenheit (1686–1736). It uses the degree Fahrenheit (symbol: °F) as the unit. Several accounts of how he originally defined his ...
.
Due to
thermal expansion
Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.
Temperature is a monotonic function of the average molecular kinetic ...
, precision
length
Length is a measure of distance. In the International System of Quantities, length is a quantity with dimension distance. In most systems of measurement a base unit for length is chosen, from which all other units are derived. In the Interna ...
measurements need to be made at (or converted to) a defined temperature. ISO 1 helps in comparing measurements by defining such a reference temperature. The reference temperature of 20 °C was adopted by the
CIPM
The General Conference on Weights and Measures (GCWM; french: Conférence générale des poids et mesures, CGPM) is the supreme authority of the International Bureau of Weights and Measures (BIPM), the intergovernmental organization established i ...
on 15 April 1931, and became ISO recommendation number 1 in 1951.
[Ted Doiron]
20 °C—A Short History of the Standard Reference Temperature for Industrial Dimensional Measurements
. Journal of Research of the National Institute of Standards and Technology, Vol. 112, No. 1, January–February 2007. It soon replaced worldwide other reference temperatures for length measurements that manufacturers of precision equipment had used before, including 0 °C, 62 °F, and 25 °C. Among the reasons for choosing 20 °C was that this was a comfortable and practical workshop temperature and that it resulted in an integer value on both the Celsius and Fahrenheit scales.
See also
*
Metre
The metre (British spelling) or meter (American spelling; see spelling differences) (from the French unit , from the Greek noun , "measure"), symbol m, is the primary unit of length in the International System of Units (SI), though its pref ...
*
International Organization for Standardization
The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Ar ...
References
{{ISO standards
#00001
Temperature
Quality control