The cryogenic apparatus and techniques used to calibrate 3 platinum‐encapsulated 4‐lead germanium resistance thermometers for use in precision calorimetry from 1 to 25°K are described. The calibration data for each thermometer were fitted with the aid of a digital computer by a polynomial expressing logRin terms of powers of logT. The sensitivity and temperature‐cycling stability of these thermometers were adequate to recommend this type of temperature sensor for accurate low temperature calorimetry. A test of the temperature scale and of an isothermal type calorimeter was made by measuring the heat capacity of a sample of 99.99+% copper from the 1965 Calorimetry Conference Copper Standard and comparing the results with those obtained by other investigators. An equation to represent the heat capacity of pure copper from 1 to 25°K, based upon appropriate literature results and the present data, is offered as a convenient copper reference equation for intercomparison of heat capacity results from various laboratories.