Abstract: Apparatus comprising a measurement-transmitting unit with two outputs to generate a time sequence of voltage values containing a measured size to be averaged; a mean value-forming unit which has two inputs connected respectively to the two outputs of the measurement-transmitting unit, and a resistor-capacitor network for continuously averaging the voltage values fed to it by the measurement-transmitting unit, the resistor-capacitor network including a capacitor which is connected across the two inputs of the mean value-forming unit via at least one resistor and at least one controllable switch; and a program-control unit connected to said at least one controllable switch and having means to control said at least one controllable switch in such a way that, during at least some of the averaging processes, the capacitor is connected to the two inputs of the mean value-forming unit, via said at least one resistor, for a switching time T.sub.i, which fulfills the condition T.sub.i =RC 1n (i/(i-.sub.