A variable-interval timer

A variable-interval timer with an audible tone output was designed to pace participants in human-factors studies. The timer can be operated in a continuous (recycling) mode or in a time-out (“beat-the-clock”) mode. In the continuous mode, the audible tone is emitted at the end of the preset interval and a new timing cycle is begun. In the time-out mode, the research participant must depress a switch both to avoid the tone and to begin a new cycle. The time interval can be digitally programmed for intervals from 1 sec to 2 h and 45 min. The operation of the timer is described, and construction details are provided.