Stopwatch

A timepiece that measures elapsed time from a chosen start point, typically with controls to start, stop, and reset the count.

Chronograph: A timepiece with a mechanism for measuring intervals independently of its time-of-day display. A chronograph adds elapsed-time measurement to a watch, while a stopwatch is dedicated to timing intervals.
Christiaan Huygens: A Dutch scientist who pioneered the practical pendulum clock in the seventeenth century. More precise clocks made reliable measurement of short intervals increasingly practical.
Track and field: A sport combining running, jumping, and throwing events, often measured against time or distance. Stopwatches time races and training intervals, though official results often use electronic systems.
Clock: An instrument that indicates or measures the current time. A clock gives time of day; a stopwatch measures duration from a chosen start.
Split-second timing: A timing method that records an intermediate interval without ending the overall measurement. Split timing lets a stopwatch record a lap while its main count continues.
John Harrison: An English clockmaker whose marine timekeepers enabled accurate longitude determination at sea. His portable precision timekeepers advanced the engineering behind accurate portable timing.
Swimming: The sport of propelling the body through water using coordinated movements. Stopwatches support practice timing, while competitions use automated timing systems.
Timer: A device that measures a set duration and signals when it ends. A timer usually counts toward a preset endpoint, unlike a stopwatch's elapsed-time count.
Lap timing: The measurement of successive intervals within a longer timed event. Lap timing uses repeated intermediate readings to compare portions of a race or task.
Marine chronometer: A highly accurate portable clock used to determine longitude at sea. Its precision and portability belonged to the same timekeeping tradition as mechanical stopwatches.

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