How Online stopwatch works
Stopwatch counts up from zero with millisecond precision, and lets you record named laps so you can compare split times. Start, pause, resume and reset, the controls you expect, plus a lap list you can copy. It is the tool when elapsed time is the question: how long did this task take, how do split times compare, what was the fastest lap?
This is distinct from the countdown Timer (which counts down from a preset duration and alarms at zero) and the Pomodoro timer (which follows an automated 25/5 work-break cycle). The stopwatch has no end goal, it measures however long you let it run. It uses the browser's high-resolution Performance API, so switching tabs and back does not lose time, since elapsed duration is computed from timestamps rather than counted ticks.