Abstract: Calibrating errors of a variable gain amplifier used in an AC calibrator or a meter for measuring AC is determined for a gamut of frequencies. The gain of the variable gain amplifier is varied by adjusting the value of a variable resistor in discrete steps. A variable amplitude signal is applied to the amplifier while the resistor is adjusted in discrete steps so the amplifier derives a gamut of variable amplitude signals that are supposed to have predetermined values. The amplitudes of the gamut of variable amplitude signals derived by the amplifier are detected and compared with the values that the signals are supposed to have to derive a calibrating error signal of the amplifier for each variable resistor value. A gamut of variable frequency, constant amplitude signals is applied to the amplifier while the amplifier gain is constant. The amplifier has a tendency to derive an AC output signal having a different amplitude in response to different ones of the frequencies.