Abstract: A thermostat for cyclically regulating actual ambient temperature, Ta, to either of two values, T1 and T2, for selectable durations. A switch allows T1 to be selected and deselected and a sensor detects Ta, while a controller is connected to the switch and the sensor. The controller is capable of defining T1 and T2 values. The controller further has a memory to store a cycle period duration, a detector to detect when the switch selects or deselects T1, and a timer which establishes T1 duration based on the time between T1 selection and deselection, and establishes T2 duration as at least a portion of the remainder of the cycle period. The controller automatically cyclically repeats the established T1 and T2 durations during each cycle period until T1 is again selected by the switch. A signal generator in the controller generates a control signal corresponding to the difference between Ta and T1 or T2 during their respective durations.