In order to minimize the transient effect associated with switching a constant current power supply to different loads, a break‐before‐make type of switch contact arrangement is shown to be preferable to a make‐before‐break type of arrangement. Series resistance in the load circuit may be required for low current applications. With a constant heater current, the average heater power for the entire heating period can be precisely determined as the product of the current and the mean value of two particular potential readings. These two readings, symmetrical about the midpoint of the heating period, should be taken at specified intervals as determined by the exponential heat conduction characteristics of the calorimeter assembly.