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ISO 1 is aninternational standard set by theInternational Organization for Standardization that specifies thestandard reference temperature forgeometrical 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 tothermal expansion, precisionlength 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 theCIPM 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 aninteger value on both the Celsius and Fahrenheit scales.
It was the first ISO standard, issued originally asISO/R 1, anISO Recommendation.[3]
| Preceded by — | Lists of ISOs ISO 1 | Succeeded by ISO 2 |
