Abstract: A three-mode analog controller for regulating a signal corresponding to a controller variable to produce a controller output, comprises an integrating circuit, a proportional circuit, and a derivative circuit. The integrating circuit includes a reset adjustment for varying a time constant thereof, the proportional circuit includes a gain adjustment for varying the gain thereof and the derivative circuit includes a rate adjustment for adjusting the rate of derivation of the signal. The gain adjustment comprises a photoresistor associated with a source of light which is provided with varying current corresponding to the signal to vary the resistance of the photoresistor and, thus, the gain value. The reset and rate adjustments may also comprise photoresistors with light sources or may be formed of field affect transistors each controlled by a circuit and remotely located potentiometer or variable voltage source.