RE: notes on 320 CSS Pixels to inches

> And this specific discussion is why I have such a hard time understanding why we don't define the user's perceived physical, on screen size of the button as the minimum in the SC.

Because in a *web content* context, the author has no control over that, and it is un-testable (or rather, everyone would get different results).

Browsers primary measure of content is CSS pixels. Under the hood all the other measures (including CM, Em etc) get converted to CSS pixels for rendering, then device pixels for display. That conversion from CSS to device pixels is where the manufacturer/browser decides how big things should appear on that screen. 


>   The majority of the research (and I've spent the past few days looking at over 500 pages of research studies on touch and target size) describe the stimulus used as the target in millimeters (aids replicability of research).
>  The human engineering design guidelines used in aerospace or the accessibility design guidelines for elevator controls define button size as a physical measure. 

That makes sense in a research setting, or where you build the hardware, you can measure and control that.


>  When we talk about CSS Pixels, and define minimum target size in terms of pixels in a world of many display sizes and true pixel densities, there appears to be a broad acceptance that, yes, there is a fudge factor...

When talking about the reflow SC the measure makes more sense as it is about viewing, not touching. So having a CSS Pixel that is 5 times as big on a TV compared to a phone makes sense, as your viewing distance is greater. 

If you are looking at devices between mobile phones and desktop monitors (e.g. Surface pro, the larger iPad pro), the fudge factor is a lot higher because they are generally held at arms length (or assumed to be), so I'd *guess* that hitting targets is actually harder than a mobile held close?

The other fudging factor is that size is a continuum. The bigger the target the better. All research will find that, it's called Fitt's law (one of the few in psychology). But saying 'as big as possible' is not testable. We need some sizes.

Defining the target size in CSS pixels is necessary, there is no other cross platform measure. However, I'm not sure the target-size SC works as it is.
We need to explore the impact of spacing, and work out some justifiable sizes.

-Alastair

Received on Thursday, 18 January 2018 15:13:11 UTC