Stopwatch accuracy test: can you stop it at exactly 10.00?

How the test works

Press once to start the stopwatch and once to stop it. Each try counts how far from the target you stopped, in milliseconds, early or late. After 5 tries you get your average miss, your closest try and whether you tend to stop early or late. A try is marked when the clock read the target exactly, such as 10.00.

Shown clock or hidden clock

With the clock shown, you watch the numbers run and stop on the target: it tests how well you time a press to something you see coming. With the clock hidden after its first second, you count in your head: it tests your sense of time. Each setting keeps its own best on this device.

Why stopping at exactly 10.00 is hard

The clock shows hundredths, so 10.00 is on it for only 10 milliseconds. A 60 Hz screen draws a new picture every 16.7 milliseconds, so it skips some hundredths altogether: in a run you may never see 10.00 drawn. The test times your press, not the picture, so a stop at 10.004 still reads 10.00. See what your screen draws with the refresh rate test.

What the browser cannot measure

The times are the browser’s own timestamps for each press, rounded to 0.1 ms in Chrome and to 1 ms in Firefox and Safari, more when Firefox resists fingerprinting. The browser cannot see your finger move, only the moment each press reaches the page. Your keyboard, mouse or touch screen delays the start and the stop alike, so most of that delay cancels out, unlike in the reaction time test. What is left is how much it varies from press to press.

Sources: MDN, Event.timeStamp and requestAnimationFrame; W3C, High Resolution Time. The scoring rules are our own.