铁路春运绘出美丽画卷
 | This article needs additional citations for verification. (July 2009) |
ISO 1 is an international standard set by the International Organization for Standardization that specifies the standard reference temperature for geometrical product specification and verification. The temperature is fixed at 20 degrees Celsius (°C), which exactly equals both 293.15 kelvin (K) and 68 degrees Fahrenheit (°F).[1]
Due to thermal expansion, precision length 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 on 15 April 1931, and this temperature was used in ISO recommendation number 1 in 1951.[2] It soon replaced worldwide other reference temperatures for length measurements that manufacturers of precision equipment had used, 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.
It was the first ISO standard, issued originally as ISO/R 1, an ISO Recommendation.[3]
See also
[edit]| Preceded by — |
Lists of ISOs ISO 1 |
Succeeded by ISO 2 |
References
[edit]- ^ "ISO 1:2016 - Geometrical product specifications (GPS) -- Standard reference temperature for the specification of geometrical and dimensional properties". Iso.org. 2025-08-14. Retrieved 2025-08-14.
- ^ Ted Doiron: 20 °C—A Short History of the Standard Reference Temperature for Industrial Dimensional Measurements Archived 2025-08-14 at the Wayback Machine. Journal of Research of the National Institute of Standards and Technology, Vol. 112, No. 1, January–February 2007.
- ^ Tranchard, Sandrine (2025-08-14). "ISO celebrates 70 years". ISO. Retrieved 2025-08-14.
