The pi is either emitting a mouse move or detecting one on the physical device and measuring the time that passes until the photo diode/resistor (not an led) is detecting the cursor to move away.

It's essentially the same setup you would use to detect input to photon latency if you don't have a high speed camera.

Edit: Ah no there's another setup with a pi pico in there... Yeah it's binding and LED Lighting up to a button press to have two visual indicators (LED and Cursor Reaction) you can measure using a high speed camera. Them only having a 90fps phone camera makes it means the measurements are only in 11ms increments though.

[–] [email protected] 1 points 1 week ago

will try again with a photodiode instead, since it's known to be a valid way to measure stuff like this, and it seems precise enough at that

if it isn't this, then I'll probably have to dig into libinput or something