Recommendation 3 of the 85th CIPM (1996)

Temperature scale below 1 K

The Comité International des Poids et Mesures,


  • that many important research activities are in progress at temperatures below 1 K,
  • that these researches require an accepted temperature scale which c1osely represents thermodynamic temperatures,
  • that the ITS-90 3He vapour pressure equation is believed to deviate from thermodynamic temperatures between 1 K and its lower limit of 0,65 K, noting that several discrepant laboratory scales below 0,65 K have been developed,


  • that the deviation of the ITS-90 3He vapour pressure equation from thermodynamic temperature below 1 K be further investigated,
  • that research be undertaken to resolve discrepancies between existing 3He melting pressure scales,
  • that national laboratories collaborate to develop a 3He melting pressure equation to serve as the basis for an extension of the ITS-90 down to a temperature of about 1 mK.

reference The reader should note that the official version of this Resolution is the French text

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