Is this a reaction time test?
No. This is a time-estimation game. A target time is shown, you click when you judge that time has elapsed, and the drill reports your timing error in milliseconds. To measure how fast you react to a signal, use the Light Reaction Test.
How does the stop the timer game work?
A target time appears for a moment and then disappears. A glowing orb with no numeric readout runs while the clock counts in the background, and you click when you think the target time has passed. The drill then shows the exact time you clicked and your error.
How long are the target times?
Targets start between 1 and roughly 2 seconds, and the upper limit rises with your level up to a maximum of 8 seconds. The target is shown with three decimals, for example 3.250s.
How is the score calculated?
Your error is your click time minus the target time. A click counts as a hit when the error is within 50 ms plus 5% of the target, so a 3-second target allows 200 ms. Closer clicks earn more points, an error under 10 ms is rated EXACT, and consecutive hits raise a combo multiplier up to 3.0x.
What happens if I click too early or too late?
Both count as error. A click outside the allowed window is a miss: it resets your combo and flashes a red alert, but your score is kept.
Can I count in my head?
Yes, counting is your own strategy. The orb has no numeric readout, and its rings pulse once per second, which you can use as a beat. Try different methods and keep the one that gives the smallest average error.
Does refresh rate or input lag affect the result?
Slightly. Clicks are timestamped with the browser's performance.now() clock, but your display shows a new frame every 16.7 ms at 60 Hz, 6.9 ms at 144 Hz and 4.2 ms at 240 Hz, and input devices add polling delay (Woods et al., 2015). Compare scores on the same device.
Can practice improve my timing?
Practice usually improves performance on the task you practise, so your average error on this drill is likely to shrink. How far that carries over to other tasks varies and is not guaranteed.
Is this the same as the 10 second challenge?
It is a similar idea, judging an interval without a visible clock, but the target changes every round and is not fixed at 10 seconds. It also scores the size of your error rather than a single pass or fail.
Is it free, and does it work on mobile?
Yes, it is free with no sign-up or download. It runs in a mobile browser, but touch input adds its own latency, so compare scores only against other attempts on the same device.