Reaction time challenge

The challenge measures simple reaction time: one signal, one response, nothing to decide. You know what's coming and what to do; you just don't know when. Your number covers the whole chain, from your eyes noticing the green to your finger landing, plus the time your screen, touchscreen or mouse and browser take.

• Each run has five rounds. Before every green, the pad waits a random time between 1.5 and 4.5 seconds, so the rhythm can't be learned.
• The clock starts when the green is actually drawn on your screen, not when the game asks for it.
• Your score is your middle round, the median, so one lucky tap or one slow moment can't decide it. The result also shows your fastest round.
• Your best score is kept in this browser only, so you can try to beat it next time.

Some rounds are repeated rather than scored, so a bad round can't spoil a run and a lucky one can't fake it.

• Tapping before the pad turns green is a false start. The round is repeated, and after five false starts the run begins again.
• A time under 100 ms is treated as a guess, since nobody reacts that fast, and the round is repeated.
• A time over 2 seconds doesn't count either, and the round is repeated.
• If the page loses focus or you switch tabs during a round, the round is repeated, because a background tab can't be timed fairly.

• Use the same device each time if you want to compare scores. A phone and a laptop add different delays.
• Play when you can watch the pad without interruptions, with notifications off.
• Keep your finger just above the screen, or rest it on the space bar on a computer.
• Wait for the green. Guessing only earns false starts.