A tally counter is a mechanical, electronic, or software device used to incrementally count something, typically fleeting. One of the most common things tally counters are used for is counting people, animals, or things that are quickly coming and going from some location.
A tally counter is usually made of metal and is circular in shape. Part of the circle is flattened out and contains a piece of clear plastic. Inside the counter are a number of rings with the numbers from 0 to 9 in descending order going clockwise. Most counters have four such rings, allowing the user to count up to 9999. A metal ring may be attached to aid in holding the counter, and usually half the ring is bent to fit flush with the counter.
The counter is activated by pressing a button located above the screen. This will cause the first ring to advance one number. When the count has reached 0009, then the second ring will be advanced one click and the first ring will come back to zero. To reset the counter, a knob is located on the side. This knob turns all the rings which are displaying the same number (usually zero). When the number displayed reaches the number on the remaining rings, then they will turn too, until the display is reset back to 0000.
Electronic tally counters are available, which use an LCD screen to display the count, and a button to advance the count. Some also have a button to decrement the count, for example if a mistake is made, or if counting a majority.