The triple point of water is 273.16K. Supposing 1/273.16 = 1K and taking some other easily obtainable points, the Internatinal Committee of Weights and Measures recognised a temperature which is called International scale of temperature.

The thermodynamic scale or absolute scale first suggested by Lord Kelvin is the standard scale of temerature and is found in good agreement with the perfect gas scale. As it is difficult to realise the thermodynamic scale practically, the International Committee of Weights and Measures in 1927 (and later in 1948) found it necessary to adapt a practical known as International temperature scale. It is easily reproducible with accuracy, as it is based on a number of easily reproducible fixed points. The international scale of temperature is the nearest practical approch to the Kelvin scal of temperature.

The fixed Points given by the Internatinal Committee in 1990 are:

  1. Triple point of neon = 24.5561 K
  2. Triple point of oxygen = 54.35 K
  3. Triple point of water = 273.16 K
  4. Triple point of mercury = 234.315 K