TABLE OF CONTENTS The unit of the fundamental physical quantity known as thermodynamic temperature, symbol T, is the Kelvin, symbol K, defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. [ ]
Because of the way earlier temperature scales were defined, it remains common practice to express a temperature in terms of its difference from 273.15 K, the ice point. A thermodynamic temperature, T, expressed in this way is known as a Celsius temperature, symbol t, defined by:
The unit of Celsius temperature is the degree Celsius, symbol C, which is by definition equal in magnitude to the Kelvin. A difference of temperature may be expressed in Kelvin or degrees Celsius.
The International Temperature Scale of 1990 (ITS-90) defines both International Kelvin Temperatures, symbol T 90, and International Celsius Temperatures, symbol t 90. The relation between T 90 and t 90 is the same as that between T and t, i.e.:
The unit of the physical quantity T 90 is the Kelvin, symbol K, and the unit of the physical quantity t 90 is the degree Celsius, symbol C, as is the case for the thermodynamic temperature T and the Celsius temperature t.
The International Temperature Scale of 19901 was adopted by the International Committee of Weights and Measures at its meeting in 1989, in accordance with the request embodied in Resolution 7 of the 18th General Conference of Weights and Measures...
