stopwatch

A stopwatch is a portable timepiece designed to measure elapsed time with a dedicated display for the duration between a start and stop action. Modern stopwatches can be mechanical or electronic, and many models include features such as split times, lap memory, and countdowns. They are used in sports, science, and industry to precisely time short intervals.

The concept evolved from early portable clocks and the invention of the mechanical chronograph. In 1821, Nicolas Mathieu Rieussec introduced the first practical chronograph to time horse races, using ink on a dial. Over the 19th and 20th centuries, dedicated stopwatch mechanisms appeared in pocket watches and pocket-sized instruments. The advent of quartz in the 1960s and digital electronics in subsequent decades greatly increased precision and features.

Most stopwatches operate by engaging a gear train or electronic oscillator when the user presses a start control. An analog model typically shows elapsed time with a rotating dial and a stop/reset button. Digital stopwatches provide numeric readouts of hours, minutes, seconds, and fractions of a second. Common functions include split or lap timing, recorded times, and, in some models, auto-start or countdown modes.

Accuracy varies by mechanism: mechanical stopwatches commonly measure to tenths or hundredths of a second; modern digital units can reach thousandths of a second. They are widely used in athletics, track events, swimming, laboratory experiments, and industrial processes to timestamp durations and intervals.