Abstract: In a method of keeping time by counting the cycles of an alternating current source and providing both alternating and direct current power from the alternating current source, the direct current power including a variable display voltage for illuminating the lights, displaying time using a plurality of lights and windows corresponding to the lights, generating signals from the alternating current source, counting and dividing the signals, decoding the counted and divided signals, and lighting the lights and windows in accordance with the decoding to display the time of day, and correcting, when necessary, the time displayed by the clock, the improvement comprising providing a plurality of electrical switches corresponding to the lights, the correcting being accomplished by actuating one of the switches, completing an electrical circuit upon such actuation of the switch and comparing the display voltage with the voltage applied to the light whose corresponding switch is actuated, the comparing being operative