A typical adult reaction to a visual signal lands between 200 and 250 milliseconds. Under 200 is genuinely quick, and the low 100s is around the floor of human capability — below about 100ms you are almost certainly anticipating rather than reacting.

For scale, most of that time is not decision-making. Light hits your retina, a signal travels to the visual cortex, a motor command travels back down to your finger, and the finger moves. The thinking part is a small slice of a mostly mechanical delay.

If the wait were always three seconds you would learn to tap at three seconds, and the test would measure your sense of timing instead of your reaction. Randomising it between two and five seconds makes anticipation useless.

This is the same reason athletics uses a variable hold before the starting gun, and why a sprinter who moves within 100ms of it is ruled to have false-started — that is faster than a human can respond, so they must have guessed.

Rest your finger lightly on the screen or button rather than holding it above — the distance your finger travels is part of your measured time. Keep your eyes on the panel rather than glancing at the timer or the round counter.

The tempting mistake is trying harder. Tensing up makes reactions slower, not faster. A relaxed hand and steady attention beat coiled anticipation, which mostly produces early taps that cost you the round.

Simple reaction time is a real measure of nervous-system speed, and it varies more than most people expect: it is measurably slower when you are tired, dehydrated, or several hours past your usual bedtime. Testing yourself at the same time of day is the only way to compare runs honestly.

It also declines gradually with age from the early twenties, which is normal and not something practice reverses. You can shave off a few milliseconds by learning the task, and after that your score is mostly telling you how well-rested you are.