ISO 1 Geometrical Product Specifications (GPS)- Temperature for Geometrical Product Specification & Verification
ISO 1 is an international standard set by the International Organization for Standardization that defines the standard reference temperature for geometrical product specifications and verification. The temperature is fixed at 20 °C, which is equal to 293.15 Kelvin and 68 degrees Fahrenheit.
Due to thermal expansion, precise length measurements need to be made at (or converted to) a specific temperature, ISO 1 helps to compare measurements by defining such reference temperature. The reference temperature of 20 °C was accepted by the CIPM on 15 April 1931 and became ISO recommendation number 1 in 1951, it soon replaced worldwide other reference temperatures for length measurements that manufacturers of precision equipment had been 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
If you are looking for more support with your certification,