How This Test Works
The box waits a random delay (to prevent guessing the timing), then turns green — the timer starts at that exact moment using your browser's high-precision performance.now() API, and stops when you click. Clicking before the box turns green counts as a false start and doesn't record a time, since it isn't measuring a real reaction. This is a fun, approximate test of visual reaction time — not a clinical measurement, since actual results are also affected by your device's display refresh rate and input latency.