Latencies bellow 16ms require a refresh rate higher than 60Hz.
For 9ms you need at least 90Hz. Don't know many who do that. Specially if you take in consideration the battery hit that the faster update rate requires.
In the worst case 60Hz + this new pen will add up to (16 + 9) 15ms of latency, right?
If the screen refreshes at T=0,16,33,50 and you create input at T=8 then the input will be processed at T=17 (8+9), so you will need to wait for T=33 before it show up for a total latency of 25ms (33-8).
Which is a lot better than the potential total latency of 36ms with a 20ms pen.
Refresh rate isn't latency. Though you are right that you do have to wait for the screen to redraw.
There is screen latency as a completely separate number though, and those would add up. Many lcd monitors can have up to a 20ms latency. And those numbers would add up like you suggest. It's why gaming monitors can charge a bunch for their 1ms latency at 60hz.
It is also possible to have 120hz and 20ms latency. The numbers are not related.
No, refresh rate directly affects latency. At a refresh rate of 60Hz (without gsync/freesync), with input arriving at arbitrary times, you have an average of half a frame (and a maximum of a whole frame) of unavoidable latency, above and beyond whatever other latency may exist.
If you have enough control over your devices, you can arrange for your input to arrive at just the right time to be included in each frame without extra latency, though.
The kind of latency you describe is that internal to the display; it could be called the video-signal-to-photon latency. The parent you're replying to is explaining the action-to-video-signal and compute-to-video-signal latency, and its effects on the action-to-photon latency.
Well I didn't even consider any latency of the screen itself.
But someone please explain how a refresh rate less than infinity doesn't create some sort of delay. In my naive understanding a 60Hz monitor means it refreshes the screen every 16ms. If you miss one refresh, you'll have to wait 16ms for the next one. This would be an extra 16ms it takes between moving the pen and seeing the reaction, right?
Yeah I was going to say. The iPad Pro display has a 120hz refresh rate and it's highly noticeable, and IMHO far superior to any other mobile device display.
For 9ms you need at least 90Hz. Don't know many who do that. Specially if you take in consideration the battery hit that the faster update rate requires.