Reaction time test
Test
Click before the signal and that round runs again. Five rounds make an average.
Results
Your best stays in this browser.
What a reaction time measures
It is the time between the screen changing and your click. The unit is the millisecond (ms), and 1000ms is one second. Seeing the signal, deciding, and moving your finger all happen inside that number.
What happens if I click too early
That round is not recorded and runs again. The wait before the signal is picked at random between 1.2 and 3.5 seconds each round, so counting out a rhythm and clicking on it mostly lands you on this screen.
Where the record is kept
Only your best time is kept, in this browser's storage. It is not sent to a server and it is not compared with anyone else's. If storage is blocked, the best time is the only thing lost — the test itself still runs.
Why the number differs between devices
How long a screen takes to draw a new frame, and how long a touch or mouse signal takes to reach the browser, differ from device to device. The same person gets different numbers on a laptop and on a phone. Comparing your own runs on one device says more than comparing devices.
How is the share link built
Share puts the numbers into the address and builds a link. Opening that link fills the same card with those numbers, and the person who opened it can start their own round right away. Building a link sends nothing anywhere, it only writes an address.
The address is scrambled so the values are not readable, and changing one character stops the numbers from showing. That catches links garbled in transit or edited by hand. It does not confirm who measured the value, or when.