Indicator

An indicator is a small hand-held device that allows the home plate umpire to keep track of balls, strikes and outs. The most common type of indicator has three buttons on the side, one for each element of the count; pushing the appropriate button after a pitch or an out allows the machine to display the proper number. The umpire then only has to glance at the display to know what the situation is. He then resets the first two buttons at the beginning of every new at-bat, and the third one after each half-inning is completed.

Umpire Bill Betts is credited for creating the first indicator in the 1890s; his invention was adopted by the National League in 1895.