This instrument has two function, as a timer and as a counter. This apparatus is used together with Air Track (PMK 140 or PMK 150), Atwood Machine (PMK 135), Free Fall Apparatus (PMG 140), Reversible Pendulum (PMG 125), Moment of Inertia Apparatus (PMK 380) and other experiment which need a high accuracy otomatic and precision time measurement.

Timer Counter is used together with photo gate(s) which acts as a sensor to detect the transition from light to dark and from dark to light at the time an object passes through the gate(s).

There are two kind of Timer Counter, AT-01 and AT-02 where the second one has more feature.