Stopwatch

Worked example

Started, then checked again 90 seconds later, elapsed time reads exactly 1:30, recomputed fresh from the original start moment rather than accumulated tick by tick. Pause it right at that 90-second mark, wait an untracked 5 minutes, then resume, and the display still reads 1:30 at the moment of resuming, since the entire paused interval is excluded from the running total.

Common mistakes

• Expecting the stopwatch to keep running if the tab is closed. It only tracks time while the page stays open, whether in the foreground or backgrounded.
• Assuming a long gap between checks introduces drift. Elapsed time is recomputed fresh from the original start each time, so no amount of backgrounding causes it to fall behind.

Limitations

This is a browser-local utility, not a precision timing instrument suited to competitive or scientific use. A refresh clears the running total completely, since nothing about it is saved between page loads.