how a reaction time test works
The millisecond number that shows up after you click is not your raw neural reaction, it is that reaction plus several delay layers added by the browser and the screen itself. This page explains the stopwatch behind the test, where that extra delay comes from, and how the tool handles early clicks without polluting your average.
An early click never produces an artificially low number, the code discards the attempt and restarts just that round with a new random delay.
The sum of the 5 times is 1135, divided by 5 gives 227, and the tool rounds that value with Math.round before displaying the session average.
The color change can be ready in code before the next frame is drawn, so it only appears on screen at the following frame, adding up to 16.7ms to the measured time.
It's the gap between perceiving a stimulus (the screen turning green) and responding to it (the click). It includes the time for the signal to reach the brain, be processed and trigger the hand movement.
Because the wait varies between 1500 and 4500 milliseconds precisely to stop you from clicking by rhythm without actually watching the color change. A fixed delay would let you memorize the moment and click ahead of time, invalidating the measurement.
Because the phase switches to "too soon" instead of recording a near-zero time, and the same round is redrawn from scratch. That stops a lucky or impatient click from artificially dragging your average down.
No, the number includes screen latency up to a full frame of delay at the refresh rate, input device latency, and the time the browser takes to dispatch the click event. The result measures "stimulus to registered event", always somewhat larger than the purely neural reaction.
At 60 Hz, each frame takes about 16.7 milliseconds; the switch to green can be ready in code and still wait until the next frame is drawn to actually appear on screen, adding up to that amount to the total measured time.