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Comment by half-kh-hacker | Hacker News Reader

The methodology of the linked keyboard latency article including the physical travel time of the key has always irked me a little

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Yet as a lover of Cherry Reds and Blues, in my opinion that time should most definitely be included. I am not a gamer, but I do notice the difference when I'm on a Red keyboard and when I'm on a Blue keyboard.

My initial gut reaction to this was - yeah, of course. But after reading https://danluu.com/keyboard-latency/ - I'm not so sure. Why exactly should physical travel time not matter? If a keyboard has a particularly late switch, that _does_ affect the effective latency, does it not?

I can sort of see the argument for post actuation latency in some specific cases, but as a general rule, I'm struggling to come up with a reason to exclude delays due to physical design.

We don’t all press keys in exactly the same way. How would you control for the human element?

Variance isn't a reason to simply ignore part of the problem.

It's a personal choice of input mechanism that you can add to the measured number. Also, the activation point is extremely repeatable. You become fully aware of that activation point, so it shouldn't contribute to the percieved latency, since that activation point is where you see yourself as hitting the button. This is the reason I don't use mechanical keyboards; I can't activate the key in a reasonable time.

>This is the reason I don't use mechanical keyboards; I can't activate the key in a reasonable time.

From what I understand, non-mechanical keyboards need the key to bottom out to actuate, whereas mechanical switches have a separate actuation point and do not need to be fully pressed down. In other words mechanical switches activate earlier and more easily. What you said seems to imply something else entirely.

If you're comparing a mechanical key switch with 4mm travel to a low-profile rubber dome with 2mm or less of travel, the rubber dome will probably feel like it actuates sooner—especially if the mechanical switch is one of the varieties that doesn't provide a distinct bump at the actuation point.

No, I’m speaking only of travel required to activate the key. There’s still travel to the activation point for mechanical keyboards. I’ve yet to find a mechanical switch with an activation distance as small as, say, a MacBook (1 mm). Low travel mechanical switches, like from Choco (as others have mentioned) are 1.3mm. Something like a Cherry Red is 2mm.

There are mechanical switches with near 1 mm travel, comparable to laptop keyboards. E.g. Cailh choc switches have 1.3 mm travel.

(I would love to see scissors-action keys available to build custom keyboards, but I haven't seen any.)

A lot of modern keyboards allow you to swap out switches, which means switch latency is not inherently linked to a keyboard.

It also completely ignores ergonomics. A capacitive-touch keyboard would have near-zero switch latency, but be slower to use in practice due to the lack of tactile feedback. And if we're going down this rabbit hole, shouldn't we also include finger travel time? Maybe a smartphone touch screen is actually the "best" keyboard!

Latency isn't everything; but that doesn't mean it's irrelevant either. I'm OK with a metric that accurately represents latency with the caveat that feel or other factors may be more important. If key and/or switch design impacts latency in practice; shouldn't we measure that?

I guess that is an open question - perhaps virtually all the variance in latency due to physical design is tied up with fundamental tradeoffs between feel, feedback, sound, and preference. If so - then sure: measuring the pre-activation latency is pointless. On the other hand, if there are design choices that meaningfully affect latency without meaningfully impacting other priorities, or even where gains in latency are perhaps more important than (hypothetically) small losses elsewhere - then measuring that would helpful.

I get the impression that we're still in the phase that this isn't actually a trivially solved problem; i.e. where at least having the data and only _then_ perhaps choosing how much we care (and how to interpret whatever patterns arise) is worth it.

Ideally of course we'd have both post-activation-only and physical-activation-included metrics, and we could compare.

I'm fine with wanting to measure travel time of keyboards but that really shouldn't be hidden in the latency measurement. Each measure (travel time and latency) is part of the overall experience (as well as many other things) but they are two separate things and wanting to optimize one for delay isn't necessarily the same thing as wanting to optimize both for delay.

I.e. I can want a particular feel to a keyboard which prioritizes comfort over optimizing travel distance independent of wanting the keyboard to have a low latency when it comes to sending the triggered signal. I can also type differently than the tester and that should change the travel times in comparisons, not the latentcies.

Because starting measuring input latency from before the input is flat out wrong. It would be just as sensible to start the measurement from when your finger starts moving or from when the nerve impulse that will start your finger moving leaves your brainstem or from when you first decide to press the key. These are all potentially relevant things, but they aren't part of the keypress to screen input latency.

Yeah that is definitely something that shouldn’t be included

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