Reaction time: what the number actually includes
Every reaction-time site hands you a number as if it were a property of your body. It isn't. It's a property of a chain: photons leave the panel, your retina catches them, the brain decides, the finger drops, the switch closes, the mouse reports, the OS delivers. The tests — ours at the same address included — can only time the whole chain end to end.
Which would be fine, if the chain were the same everywhere. It's not even close.
Where the hidden milliseconds live
The display is the big variable. A page can flip a pixel to teal in code, but the panel takes its time showing it: a 60 Hz office monitor refreshes every 16.7 ms and adds processing on top — 10 to 30 ms before the color physically exists. A 240 Hz gaming panel does it in 2 to 5. That difference alone can be 25 ms — a tenth of your score, decided before you've reacted to anything.
The mouse adds its share. Wired gaming mice polling at 1000 Hz report within a millisecond; a budget wireless mouse in power-saving mode can sit on a click for 8 or more. The OS batches input events too. Small numbers, but they stack in one direction: onto your total. TVs are the extreme case — many add 50–100 ms of picture processing unless they're in game mode, which is why a reaction test on a living-room setup reads like a concussion.
The part that's genuinely you
Strip the hardware away and the human baseline for a visual cue sits around 180–220 ms for young, alert adults. Auditory reaction runs about 40 ms faster, which is why races start with a bang instead of a flash. Below 100 ms to sound, officials call it a false start — the body literally can't do it; anything quicker was a guess already in motion.
Age drifts the number upward slowly. Fatigue, alcohol and distraction move it faster than age ever will — the same person swings 30–50 ms between sharp mornings and late nights. One number never describes you; five rounds barely does, which is why our test won't score a single round.
How to use the number anyway
Same machine, same monitor, same mouse — then the hardware terms cancel out and changes are real signal. Test rested versus tired and watch caffeine work. Compare before and after switching your monitor to its high-refresh mode (a real, visible improvement). What the number can't referee is you-on-a-laptop versus your friend on a 240 Hz rig. That contest was decided at the checkout, not in anyone's nervous system.