Stopwatch & Timer

This is a browser stopwatch that counts up with centisecond (hundredth-of-a-second) resolution and offers start, pause, lap, and reset. It takes its time from performance.now(), the browser’s high-resolution monotonic clock. Monotonic means the clock only moves forward and is independent of the computer’s displayed time — if your system clock changes or syncs itself mid-run, the measurement isn’t affected.

When you press Start, the tool stores a reference timestamp; on every animation frame (typically once per screen refresh) it recomputes elapsed = now − reference and redraws the display. Pause stops the updates and keeps the elapsed value; pressing Start again re-anchors the reference to now − elapsed, so paused time is excluded exactly and nothing drifts. The display format is mm:ss.cs — an elapsed time of 83.456 seconds shows as 01:23.45 — and the minutes keep counting past 60, so 90 minutes reads 90:00.00.

Lap records the cumulative elapsed time at the instant you press it, and the list shows the newest lap first. Worked example: press Lap at 01:00.00 and again at 02:10.00 — the list shows those two cumulative times, and the second lap’s own duration is the difference, 02:10.00 − 01:00.00 = 01:10.00. Lap is only available while the stopwatch is running, and Reset clears both the clock and the lap list.

Because elapsed time is always recomputed from the stored timestamp rather than accumulated tick by tick, the reading stays correct even when the display briefly stops updating — browsers throttle animation frames in background tabs, and the readout simply snaps to the right value when you come back. The practical limit on accuracy is you: human reaction time pressing the buttons dwarfs any timer error. That makes this ideal for workouts, cooking, studying, and everyday timing, though not a substitute for certified sports-timing equipment.