PTB-96, the ultra-low temperature scale of PTB

The establishment of the ultra-low temperature scale at PTB in the range from 1 mK to 1 K, and its transfer to the He melting pressure equation, is described. The temperature scale, which has been constructed with magnetic thermometry to obtain a smooth pressure-temperature relation over a wide range, ultimately relies on primary noise thermometry. The construction and verification of the scale is discussed, and a comparison with other temperature scales is presented.