Abstract: A rate/time control device for computing an activity period. The control device includes a clock for generating a representation of present time and an element for storing a start time therein. A first input element provides an input to the storage device from the clock representative of the start time. A first output element is provided for receiving an output from the storage device representative of the start time. A time computer is included for computing the activity period by subtracting the start time from the present time.The control device further includes a rate selector and a charge computer for calculating a monetary charge for the activity period by multiplying the rate by the activity period. A plurality of the control devices may be coupled together to allow one control element to operate a plurality of units.