Mechanical counters are used to detect, totalize and indicate a sequence of events in applications that do not use electrical power. There are four basic types of products: revolution counters, rotary counters, stroke counters, and pushbutton or manual counters. Revolution counters are mechanical counters that record one count for each revolution of a shaft. Rotary counters are designed to record a specified number of counts per rotation. Stroke counters record one count for each stroke. Typically, the count stroke is measured in degrees. With rotary ratchet counters, a type of stroke counter, an internal spring returns the shaft or lever to its original position. Pushbutton counters are used for manual counting. The pushbutton is actuated by the operator and typically records one count for each actuation. Most pushbutton counters or manual counters are handheld devices. Other unlisted, specialized, or proprietary mechanical counters are also available.