When you press Lap, AnyTool records two numbers. The lap time is the duration of just that segment — the time since your previous lap — which is what you compare to spot your fastest and slowest efforts. The cumulative total (often called the split) is the whole elapsed time from Start up to that lap. The table shows both side by side, plus how far each lap sits from your running average, so you can see at a glance which segments were quicker or slower than usual.

Browsers throttle JavaScript timers and animation frames in background tabs, so a stopwatch that simply added time each frame would drift. AnyTool instead records the wall-clock moment you pressed Start and, on every animation frame, computes elapsed time as the accumulated time plus the current clock minus that start moment. If the tab is throttled or your computer sleeps, the live centisecond display freezes while hidden but the underlying total is recomputed correctly the instant the tab is visible again — so when you press Stop, the total elapsed time is right. Keep the tab open for the smoothest display.

In an active foreground tab the stopwatch is accurate to about 10 milliseconds, more than enough for workouts, cooking, study sessions, presentations and casual timing. The real limits are your own reaction time when pressing Start and Stop and your screen’s refresh rate, not the maths. Because of that — and because the page must stay open to run — it should not be used for races, scientific measurement or any official timing. Treat it as a precise everyday stopwatch, not a calibrated instrument.

After recording laps you can copy the whole table to your clipboard in one tap or download it as a CSV file ready for Excel, Google Sheets or any data tool, with each row holding the lap number, lap time and cumulative total. All timing and exporting happen client-side in your browser — there is no account, no server and nothing is sent anywhere — and the page works offline after first load.