3. Temperature: a measurable quantity

Temperature can only be measured if a unit and a reference are defined. At the various international conferences of the Bureau International des Poids et Mesures (BIPM), degrees of temperature, which could only be identified and associated with different scales (Fahrenheit, Réaumur, Celsius), were finally replaced by the kelvin (K) and the degree Celsius (°C), symbols of a measurable quantity [6] .

The definition of temperature is based on thermodynamic laws and on the convention of assigning the value 273.15 K to the triple point of water. The useful representation of these thermodynamic temperatures is provided by the approximation of the International Temperature Scale of 1990 (ITS-90), in which the temperature of a certain number of physicochemical phenomena (boiling points,...