Stopwatch
Start, stop and record laps to a tenth of a second. Space starts and stops, L records a lap, R resets.
Keyboard: Space start or stop · L lap · R reset
How it works
Each lap records two times: the lap time (how long that lap took) and the total (the time on the stopwatch when you pressed Lap). Once you have two laps or more, the fastest and the slowest are marked.
The stopwatch saves its start time in this browser, so a reload or a closed tab does not lose the running time or the laps.
Questions
It reads your device clock, which browsers update every millisecond, and shows tenths of a second. Human reaction time (about 0.2 s) is the larger error when you press the buttons by hand.
Yes: Space starts and stops, L records a lap and R resets, as long as no text field has the focus.
Yes. It works from the moment you pressed Start, so time keeps counting while the tab is in the background or even closed.