Koshin StudioStop at exactly 10 seconds!
Press start and count ten seconds in your head.
When you think it is time, stop.
Free. Runs in your browser, no install or sign-up. The screen text is in Japanese, but the game is just a start button and numbers.
What it is
The screen shows no numbers, no ticks and no sound. Between pressing and stopping, nothing moves. All you can rely on is the second hand inside you.
You stop three times and see your error from the target. Some people are off by 0.5 seconds, and some stop within 0.02. It is shown per attempt rather than as a total, because that makes your skill easier to feel. The best single attempt of the three is also kept. The average is skill; the best single is luck of the day.
Three modes
10 seconds, no hint
The basic way to play: three attempts. There is no clue at all.
10 seconds, with a hint
A clock is shown for the first 3 seconds only. Match your own beat to it and do the rest by yourself. The moment 3 seconds pass, the display disappears completely.
100 seconds, one shot
One attempt only. While you count the 100 seconds there is nothing to do. If you leave the screen (switch tabs or the screen turns off), that attempt becomes invalid.
Why three decimals
Browser clocks differ in coarseness by device. performance.now() is deliberately made less precise as a Spectre countermeasure: Chrome in 5 µs steps, Safari and Firefox in 1 ms steps.
If six decimals were shown, a device with a coarser clock would more often end in 000 and gain an advantage. In a game about being “exact,” the luck of your device would decide the ranking. So I cut at three decimals to put every device on the same ground.
Nothing moving
While building it, I once put a blinking lamp somewhere in the display. It became a stand-in metronome. If something flashes at 1 Hz in your sight, people can count along with it, and a game about counting by yourself vanishes entirely.
Now there is nothing that moves periodically during measurement: no pulsing buttons, no blinking, no animation. From the moment you press until you stop, the screen is completely still.
How it is made
The whole thing is one HTML file with zero external libraries. The digits are drawn as SVG polygons in a seven-segment shape, so it depends on no font either. The sound effects use no audio files and are generated on the spot.
The stop time is taken from event.timeStamp of pointerdown, because waiting for click adds extra delay. Your records stay in your device, per mode.
Development log for this game
This is the English version of the Japanese page.