Instrument 01 / milliseconds
Reaction Clock
Choose Start the wait. When the field flashes, press the large button or any non-navigation keyboard key. Responding before the flash simply begins a fresh wait.
The most recent five attempts will remain as translucent rings.
What this does not measure
This playful experiment combines browser input timing, device latency, display timing, and human response. It is not a neurological assessment or a measurement of nervous-system health. Results remain in this browser session and are not sent anywhere.
Why this clock exists
The W3C High Resolution Time specification gives web pages a monotonic clock for measuring short intervals, while browsers may reduce precision for privacy and security. This instrument uses that clock but cannot separate a person's response from display, operating-system, and input delays. Its expanding rings make the mixed measurement visible: a small duration becomes a physical-looking trace, held briefly beside four earlier attempts.
W3C High Resolution Time