New two-point calibration method for platinum resistance thermometers for the range 75-400K

In this paper we describe a new method for calibrating high quality platinum resistance thermometers to ±0.01 "C over the temperature range 75-400 K. This method requires resistance measurements at only two temperatures (liquid nitrogen and the ice point) in contrast to other methods which require measurements at four temperatures. The method is based on the invariance of Cragoe's Z-functions (resistance ratios) with respect to different high quality platinum thermometers. In addition our method uses the new International Practical Temperature Scale of 1968 (IPT-68). We checked our calibration at two intermediate temperatures (liquid oxygen and the fusion point of mercury) and measured deviations of less than ±0.01°C from our calibration.