Standard Platinum RTDs
The ITS-90 (International Temperature Scale of 1990- used as a worldwide practical temperature scale in national metrology labs like NIST, NPL) is made up of a number of fixed reference points with various interpolating devices used to define the scale between points.
A special set of PRTs, called SPRTs, are used to perform the interpolation in such labs over the ranges 13.8033 K (Triple point of Equilibrium Hydrogen) to the Freezing point of silver, 971.78 ºC.