Lap versus split: what the two columns mean
Press Lap and the stopwatch records two numbers. The lap time is how long that segment took, measured from the previous Lap press (or from Start for the first one). The split time is the running total at that moment, measured from Start. In a 400 m race run in four 100 m laps of 32 s, 33 s, 32 s and 33 s, the laps are those four numbers and the splits are 0:32, 1:05, 1:37 and 2:10.
Coaches usually watch laps to judge pacing and splits to compare with a target finishing time; the table shows both so you do not have to subtract. The newest lap is at the top, and while the stopwatch runs the current, unfinished lap is shown faintly above it.
Fastest, slowest and average
From the second lap onward the table marks the fastest lap (the smallest lap time) in green with a "fastest" label and the slowest in red with "slowest", and a line above the table gives both plus the average. The average is the total time divided by the number of laps, which equals the last split divided by the lap count. With one lap there is nothing to compare, so the marks appear only after the second.
If two laps tie, the earlier one gets the mark. Colour is never the only cue: the label and an arrow icon are there for screen readers and for anyone who does not see red and green well.
Accurate to 10 milliseconds, and why it does not drift
The display shows hundredths of a second and is redrawn on every screen refresh while the tab is visible, but the time itself is not counted in ticks. The stopwatch stores the moment you pressed Start and asks the browser's monotonic clock how much time has passed, so a slow frame, a busy computer or a throttled background tab cannot make it lose time. You can choose thousandths or whole seconds in the digits menu.
Setting the system clock back, or the small corrections of a second or two that time synchronisation makes while the stopwatch runs, do not affect it. A clock that jumps forward is treated as waking from sleep, because the browser cannot tell the two apart, so the jump is added to the elapsed time; that is also why, when the device sleeps and the monotonic clock pauses, the stopwatch notices the gap against the wall clock on your return and uses the real elapsed time.
It survives switching tabs, locking the phone and reloading
Because only the start moment is stored, the stopwatch is still right after any time away from the tab. The start moment and your laps are also saved on this device the instant they change, so if you reload the page or close the tab by accident, it comes back running, with the laps intact. Reset clears everything.
On a phone, Keep screen on (on by default) stops auto-lock while the stopwatch runs; it switches off when you pause. The tab title shows the running time to the second, so you can see it from another tab on a computer.
Keyboard shortcuts and the full-screen view
Space starts, pauses and resumes; L records a lap; R resets, but only while paused, so a stray key cannot wipe a running measurement; F opens the full-screen view with just the digits and the buttons, for a gym wall, a classroom or a stage. Esc leaves it. The shortcuts do not fire while you are typing in a text box.
On a phone the three large buttons do the same jobs. Lap is placed on the left so your thumb can hit it repeatedly while Pause stays on the right.
Copying and exporting laps
Copy puts the laps on the clipboard as tab-separated text, one lap per line with its number, lap time and split, which pastes straight into a spreadsheet or a message. CSV downloads the same table with a header, the times also in whole milliseconds for calculations, and the fastest, slowest and average at the bottom.
The file is named with the date and time of the export. Nothing is sent anywhere; the laps exist only in your browser until you reset.
Uses: running, swimming, cooking, exams and work
Running and swimming: one lap per length or per kilometre, then compare pacing with the fastest and slowest marks. Cooking: time a sear or a steep without an alarm, and lap each step of a recipe. Exams and speeches: see how long each section or speaker takes; the splits tell you whether you are on schedule. Work: lap each task to log where an hour went.
If you need a sound at the end of a fixed time, use the timer instead; for repeated work and rest rounds, the interval timer.