This International Standard is a geometrical product specification (GPS) standard and is to be regarded as a fundamental GPS Standard (see ISO 14638:2015[1]). For more detailed information on the relationship of this International Standard to other standards and the GPS matrix model, see Annex B.
The definitions of the units, including those of length and temperature, are adopted by the General
Conference of Weights and Measures (CGPM) under the authority of the Convention of the Metre. These definitions are maintained in the SI brochure.
The unit of length, the metre, is independent of temperature. The current definition of the metre[6] is based on the distance light travels in vacuum during a unit of time. However, a physical object is subject to thermal expansion and consequently, its geometrical and dimensional properties are dependent on its temperature.
Specifying a reference temperature allows the geometrical and dimensional properties of a physical object to be unambiguously stated.
