Press Start and the count begins from zero. The same button pauses it, and Start again picks up where it left off. Lap marks a moment without stopping the clock: each lap time lists under the dial, and a knot freezes on the face at the ring and angle where it happened, so a run with six laps ends as a face with six dots on it. Reset clears the count and the laps together.
The keyboard does the same three things. Space starts and pauses, L takes a lap, R resets. Nothing needs the mouse once the page is open.
The face is the timer dial run backward. A countdown here empties twenty rings from the outside in; the stopwatch fills them from the inside out, and every ring takes twice as long as the one before it: the first ring takes ten seconds, the second twenty, and so on. The row of times under the dial lists those completions, and each one darkens as it passes. The face fills slowly: all twenty rings take 121 days, and then it stays full.
The clock is anchored to your device's wall clock rather than to a ticking counter, so a tab left in the background or a laptop that went to sleep still answers with the honest elapsed time when you come back. Everything runs in your browser and nothing is sent anywhere: the stopwatch does not count toward the stats or the leaderboard, and it needs no account.
A countdown is for a span you already know: twenty-five minutes of work, seven minutes for an egg, an hour of practice. A stopwatch is for a span you do not know yet. Measuring how long a task really takes, timing sets and rests without deciding their lengths in advance, or clocking a run, a speech rehearsal, or a page of reading are all jobs for counting up. The measurement is the point: once you know how long something takes, you can set a countdown for it next time. How long things really take is a guide to doing exactly that, and every timer lists the countdowns to pick from once you know your number.