ries with a resistor which shall be designed in such a way that its resistance is kept strictly constant throughout the transient. These ponents bined with a precision potentiometer, the resistance of which shall be about 100 times larger than the sum of the resistances of the probe and the series resistor. The bridge shall be connected to a power supply which can supply 20 V and a current of up to 1 A. The digital voltmeter by which the difference voltages are recorded shall have a resolution corresponding to 6,5 digits at an integration time of 1 power line cycle. The resistance of the series resistor, R S, shall be close to the initial resistance of the probe with its leads, R 0 + R L, in order to keep the power output of the probe as constant as possible during the measurement.