Abstract: The circuit comprises an elapsed time indicating meter and a silicon-controlled rectifier, used to supply power to the meter, connected in series across the circuit's first and third terminals. Additionally, the circuit includes a small resistor connected between the second and third input terminals, that is, connected in series with the a.c. device. This small resistor receives the current through the a.c. device and the voltage across the small resistor is indicative of the operational state of the a.c. device. A variable potentiometer is connected full scale across the small resistor and the variable voltage is amplified by a common-base transistor. This amplified voltage is both rectified and filtered, serving as the SCR's gate terminal input for triggering the SCR.The potentiometer is adjustable to allow the SCR to trigger in either one of two conditions.