The Unilab 'g' by Freefall Ball (g-Ball) is a fun way to measure the acceleration due to gravity and make empirical measurements to illustrate the laws of motion. The g-Ball contains an accurate timer with millisecond resolution. Timing begins when the button is released and stops when the g-Ball hits the ground. The time of flight is displayed on a clear LCD display.Batteries: CR2032 Lithium Button Cell Batteries