International Temperature Scale of 1990 International Temperature Scale of 1990 The International Temperature Scale of 1990 (ITS–90) published by the Consultative Committee for Thermometry (CCT) of the International Committee for Weights and Measures (CIPM) is an equipment calibration standard for making measurements on the Kelvin and Celsius temperature scales. ITS–90 is an approximation of the thermodynamic temperature scale that facilitates the comparability and compatibility of temperature measurements internationally. It specifies fourteen calibration points ranging from 0.65±0 K to ±0 K (−272.50±0 °C to ±0 °C) and is subdivided into multiple temperature ranges which overlap in some instances. ITS–90 is the latest (as of 2014) of
Scale of temperature below as M. Assume the set M has the cardinality of c, then one can construct an injective function ƒ: M → R , by which every thermal system will have a number associated with it such that when and only when two thermal systems have the same such value, they will be in thermal equilibrium. This is clearly the property of temperature, and the specific way of assigning numerical values as temperature is called a "scale of temperature". In practical terms, a temperature scale is always based on usually a single physical property of a simple thermodynamic system, called