How the stopwatch works
When you press Start, the stopwatch records the current timestamp from the browser's high-resolution timer (performance.now()), which is accurate to sub-millisecond precision. Every 10 milliseconds an interval updates the display by subtracting the recorded start timestamp from the current timestamp. When you press Stop, the elapsed time is saved. Pressing Start again resumes from the saved value by adjusting the reference timestamp.
Pressing Lap records the current elapsed time as a lap entry without stopping the stopwatch. The split time (time from the previous lap to this one) and the cumulative time are both recorded. The fastest and slowest lap splits are highlighted in the lap table for easy identification.
Elapsed time = Current timestamp − Start timestamp + Previously saved time
Recalculated every 10 ms; displayed as H:MM:SS.cc.
Lap split = Current cumulative time − Previous lap cumulative time
The time taken for one lap or interval alone.