How to play
Choose either hand, left or right; select a lower, middle or full comfortable target area; then choose a speed from 1/8× to 2×. Touch or mouse is the default. Camera mode privately tracks an index fingertip in the browser after a six-second comfortable-range calibration.
Follow the single moving firefly and touch it with the on-screen pointer. Lower speeds change actual target movement. Camera calibration uses only the middle 72% of your sampled range and stores neither video nor landmarks.
Safety boundary
Use a stable seated or standing position and do not reach to your limit. Stop immediately for pain, dizziness, breathlessness or unusual fatigue; the safety-stop result earns no score or reward. This is general activity, not medical measurement, treatment, rehabilitation prescription or outcome assessment.