A stopwatch is a timekeeping device used to measure the elapsed time between a starting point and an ending point. It can be digital or analog and is commonly used for sports, timing experiments, and various other activities.

Stopwatches typically have a start/stop button to begin and pause the timer, and a reset button to set the timer back to zero. Digital stopwatches use electronic circuits and LCD displays, while analog stopwatches use a mechanical movement with hands to indicate time.

The primary functions of a stopwatch include starting, stopping, and resetting the timer. Some stopwatches may have additional features like lap time recording, split timing, and countdown timers.

A chronograph is a type of watch that has stopwatch functions as one of its features, in addition to its regular timekeeping. A standalone stopwatch, on the other hand, is designed solely for timing purposes and lacks other watch functions.

The accuracy of a stopwatch depends on its quality and the type of mechanism it uses. Digital stopwatches are generally more accurate than analog ones. High-quality digital stopwatches can be accurate to within milliseconds.