This pocket-sized digital timer has two built-in photogates that can measure time, speed and acceleration. Microprocessor control offers 0.01% accuracy. Requires 4 x AAA batteries (not included) for 2 hours continuous function. Large internal memory storing up to 20 data points. When used with an inclined plane, the acceleration results can be read directly if using 2 timers linked together (a 25mm diameter ball is required). A cable for linking up two timers so that a 4 photogate system can be quickly assembled is NOT provided.