Originally Posted by cdcd
For mechanical switches, any click latency (button-down) will come from any debounce delay.
edit: This is quite misleading. It seems you're just talking about the switch itself. But a mouse is more than just a switch, so only measuring a switch while talking about the performance of a mouse is not only fallacious but misleading and disingenuous.
For "click latency" of a mouse there are many sources of delay. From the time the physical button is making contact until the application gets the event includes: debouncing, the rest of the firmware adding delays, the transmission technology adding delays (true for both wireless and wired connections and protocols) and there's more on the PC side but I assume this is configured consistently and for best possible performance (e.g. highest supported polling rates for USB mice).
Originally Posted by cdcd
The XM1 buttons are not debounced (at least not in the traditional way), hence it is not possible to measure click latency that way. So it's exactly the opposite of what you inferred: TPU testing methodology would be fundamentally flawed if it were possible to measure click latency on the XM1. This not being possible validates and confirms the method used. Your premise 'This methodology should work for ANY mouse with a pressable button [...]' is mere conjecture and not supported by facts, therefore false, and, as such, your argument is not valid either (not to mention that this premise directly contradicts the conclusion).
You just confirmed that either "TPU is doing something completely wrong or measuring something else (see my earlier posts)".
As I have explained, when measuring time delay from a mechanical switch making contact (1) and the application receiving mouse-down event (2) it doesn't matter what happens in between. Any debouncing, processing, transmission ... delay will add to (2). That's input latency.
As the testing methodology doesn't measure this time delay directly, but instead measures relative difference between a reference and tested mouse:
(1) is used as the synchronization point for the reference and tested mouse.
Time measurements at (2) gives you the relative latency.
You cannot just call this "mere conjecture and not supported by facts" and at the same time asserting this is false without providing any evidence that it is. That's hypocritical and a logical fallacy itself.
And it looks like you again didn't understand the very simple argument: since one can measure the latency between (1) and (2) one can also use two mice to measure the relative delay for any two mice with pressable switches (1) producing a mouse-down event (2).
Since the XM1 is a mouse with a button (duh) that produces a mouse-down event (duh) the inability to produce the result means that: either "TPU is doing something completely wrong or measuring something else (see my earlier posts)".