Signal and response
When you start a round, the game waits for a random delay. During that period, the panel is in a waiting state. When the panel changes to green, the page records a high-resolution browser timestamp and asks you to respond. The next click, tap, Enter, or Space action ends that round. The elapsed time is rounded to a whole millisecond for the on-page result.
The random delay is there to discourage anticipation. A click before the green signal is visible is treated as a false start. It is not displayed as a fast reaction and it does not add a value to the five recorded rounds. You can then retry without losing a valid score.
Session calculation
After a valid response, the game keeps that score in memory on the page. Once five valid responses exist, it sorts a copy of the list to find the best and median values, and calculates the average from all five. It never substitutes a site-wide benchmark or creates a result from unplayed rounds.
The result is local to the open page. Refreshing or leaving the page resets it. There is no sign-in, public profile, score API, or server-side database for this tool. The optional copy button uses the browser clipboard only after you press it.
Why the number is not only about a person
Browser timing is useful but not perfectly isolated. Modern web browsers expose high-precision timing tools for performance measurement, while the visible result can still be influenced by display refresh, rendering, input hardware, the operating system, and mobile versus desktop interaction. A public reaction-test statistics page from Human Benchmark similarly discusses display and input latency. That is why this site describes the number as a browser-test result under a particular setup.
The design goal is clear personal feedback: a simple signal, a visible false-start rule, five recorded rounds, and no invented comparison table.