Resolution 9 of the 21st CGPM (1999)

Extension of the International Temperature Scale below 0.65 K

The 21st Conférence Générale des Poids et Mesures,

considering that

• many important research activities are in progress at temperatures below 0.65 K,
• these researches require an accepted temperature scale which closely represents thermodynamic temperatures,
• the direct measurement of thermodynamic temperature is often difficult and time-consuming at temperatures below 0.65 K down to a few millikelvin, but at temperatures much lower than this direct measurements once again become feasible,
• considerable work has already been accomplished towards the development of a temperature scale for the range from 0.65 K down to 1 mK based on the melting pressure of ³He,

invites the International Committee to prepare a ³He melting pressure equation as a function of thermodynamic temperature to serve as the basis for an extension of the ITS-90 below its present lower limit of 0.65 K.

DOI : 10.59161/CGPM1999RES9E