actuator piston 28 fig2 during each pulse cycle gain multiplier 86 provides a gain to the error signal as a function of the change in position of the controlled device as measured by the position sensor 18 during the previous clock cycle the gain in multiplier 86 is derived from signal line 120 and is updated each cycle to provide the updating capability the actual position signal on line 22 is fed via line 97 to a sample and hold circuit 98 to which is also fed a series of clock pulses via line 14c the actual position signal on line 22 is also fed to a summing junction 100 via line 102 the sample and hold circuit 98 stores therein the actual position signal at the last preceding clock pulse upon receipt of the next clock pulse the new position data is fed as an input to the sample and hold circuit and the last preceding position data is fed to the summing junction 100 via line 104 the sample and hold circuit 98 may contain a shifting register at each clock pulse the summing junction 100 thereby receives on line 102 a signal indicative of the present position of the controlled device and via line 104 a signal indicative of the position.