Lap Timer

Each press of Lap records two numbers: the split, which is the total elapsed time, and the lap, which is the time since the previous press. Below the list the page keeps the fastest lap, the slowest, the average and the spread, updating as you go. Consistency is usually the more useful measure: a runner whose 400 m laps drift from 90 to 105 seconds started too fast; a swimmer whose laps are all within two seconds is pacing well. The fastest and slowest laps are highlighted so the pattern is visible without reading every row.

1. Press Start as the athlete crosses the line or leaves the wall.
2. Press Lap (or the space bar) at every marker: each lap, each length, each rep.
3. Press Stop at the finish; the final split is the total time.
4. Use Copy to put the laps on the clipboard as tab-separated text that pastes directly into a spreadsheet, or into a message to the athlete.

Timing is taken from the browser's high-resolution clock at the instant of each press, so the precision is far better than the reaction time of the person pressing the button (typically 0.2–0.3 s). For fairness in competition, use the same timekeeper for every athlete. Hundreds of laps can be recorded in one session.

• Swimming. Lap per length; the split at 50, 100 and 200 m shows where a race is won or lost.
• Cycling and rowing. Interval sessions: lap at each effort and each recovery, and compare efforts across the session.
• Motorsport and karting. Lap times per circuit lap; the average over the last five is the practical measure of pace.
• Science and industry. Time repeated cycles of a process; the spread tells you about the process's stability.
• Speedcubing and games. Solve times per attempt, with an average that excludes the best and worst if you prefer.

For a simple start–stop measurement, the stopwatch is lighter; to convert laps and distance into pace and race predictions, the pace calculator; for timed rounds with a set length, the interval timer.