Why the hundredth of a second matters
A stopwatch that only shows seconds is useless for the things people actually time: a sprint interval, a plank hold, a chemistry reaction, a speech rehearsal. This one runs on performance.now(), the browser's high-resolution clock, which is monotonic — it does not jump when your system clock is adjusted mid-measurement.
That last point is not academic. A stopwatch built on Date.now() can gain or lose a second if the machine syncs its time while you are timing.
Laps, and what they are for
The lap button records a split without stopping the clock. Each entry shows both the lap time and the total elapsed, which is the pair you need to compare intervals — a runner wants to know that lap four was slower than lap three, not just that eleven minutes have passed.
Everything stays in the page. Nothing is sent anywhere, and once the page has loaded it keeps working with no connection at all.
Frequently asked questions
Does it keep running if I switch tabs?
Yes, the elapsed time is computed from timestamps rather than counted tick by tick, so a throttled background tab does not lose time.
How accurate is it?
It displays hundredths of a second and uses the browser's high-resolution monotonic clock. Human reaction time on the button is the real limit, not the timer.
Do I need an account?
No. Nothing is stored, nothing is sent, no sign-up.