Stopwatch

A stopwatch is a timepiece designed to measure the time that elapses between its activation and deactivation, traditionally controlled by two buttons, one to start and stop the timer and display the elapsed time, and a second to reset it to zero or to record split and lap times while the watch keeps running. Mechanical stopwatches are powered by a wound mainspring, while digital electronic stopwatches use a crystal oscillator for greater accuracy and often add date and time of day functions, with some models able to be triggered by external sensors. Stopwatches are used wherever time must be measured precisely with a minimum of complication, such as laboratory experiments and sprint events, and the function is now also built into wristwatches, cell phones, portable music players and computers.