in an analog computer, a slow change in the voltage at the output of the computing amplifier (which is taken as zero) in the absence of an input signal. It is caused by variations in the parameters of the amplifier elements caused by variations in the temperature of the surrounding medium and in pressure and humidity, by aging of the elements, and by instability of the power-supply voltage. Zero-level drift leads to errors in the operations performed by the amplifiers. Automatic compensation, correction, and stabilization are generally used to reduce zero-level drift or to eliminate its effects.