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 °C to 1085 °C). When pressure approaches zero, all real gas will behave like ideal gas, that is, of a mole of gas relying only on temperature. Therefore, we can design a scale with as its argument. Of course any bijective function will do, but for convenience's sake linear function is the best. Therefore, we define it as The ideal gas scale is in some sense a "mixed" scale. It relies on the universal properties of gas, a big advance from just a particular substance. But still it is empirical since it puts gas at a special position and thus