Abstract: A timer for measuring time spent productively in an activity, with a minimum of interference with the activity, which includes a sensor and a delay circuit. The delay circuit compensates for productive time spent in an intermittent activity which may not result in the production of energy to which the sensor is responsive, as often occurs, for instance, during the practice of performing arts. Sensors preferably are responsive to energy which can be conducted through the atmosphere, such as sound and visible light. The timer may be fabricated as a free-standing unit, included within an electronic metronome or functionally combined with a variety of equipment.