[veloxo]

FWIW, a quick ballpark test shows <30 ms minimum keyboard latency on my M1 Max MacBook, which has a 120-hz display.

  Sublime Text: 17–29 ms
  iTerm (zsh4humans): 25–54 ms
  Safari address bar: 17–38 ms
  TextEdit: 25–46 ms

Method: Record 240-fps slo-mo video. Press keyboard key. Count frames from key depress to first update on screen, inclusive. Repeat 3x for each app.

[pannSun]

How do you determine at what point the key switch is activated? Or is the travel time from start to fully depressed negligible compared to measured latency?

[chronogram]

You wire an LED to a button (like a mouse left click) and with a 1000Hz camera you can count how many frames it takes for the screen to update after the LED lights up. Repeat many times to account for being in varied stages of the refresh cycle.

Well, that's how it was done 10 years ago.

[lajosbacs]

There is a good app to help with this, "is it snappy".

[agolio]

With that method I would just double check that 240-fps slo-mo video is synced to realtime. It may be applying an unnoticeable slow-motion effect (e.g. 90% speed playback) that would throw off the results

So e.g. put a clock in the video