Re: let's bump to 10mm from 9mm

Patrick, I agree with your concern.    I've seen the number 44x44 pixels mentioned before for a minimum device independ pixel size. 

Jon

Sent from my iPhone

> On Dec 17, 2015, at 3:47 PM, Patrick H. Lauke <redux@splintered.co.uk> wrote:
> 
> For what it's worth, I think it's disingenuous to dictate a physical size "as measured on the screen", as developers don't always (in fact, practically never) have knowledge of the actual physical size of a screen and can therefore not do much in this respect. They'll be setting sizes of interface elements using CSS pixels (for web content) or points, and rely on the OS and, in the case of web content, the UA to have a sensible mapping (based on the device/OS' dpi or device pixel ratio) that translates that into actual physical dimensions.
> 
> Take an iPad and an iPad Mini ... both have the same nominal resolution in CSS pixels, but their physical screens are vastly different in size. There's no way from JS for me as developer to determine the actual physical dimensions...so if I set a particular dimension for a control the only way I can (using CSS pixels, or any other CSS unit - even "mm" - which in the end is still based on a pixel), I can't guarantee that it'll be any particular physical dimension on the screen of both the iPad and iPad Mini. And if it came to actually auditing, you could end up in a situation where you audit my content on an iPad and it passes (as holding the ruler up to the screen of the iPad you'd measure 10mm), while auditing it exactly the same way but on an iPad Mini it would fail.
> 
> I'd strongly advise that instead of talking about "mm" and "as measured on the screen", you should consider talking in terms of CSS pixels, points (see https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/MobileHIG/LayoutandAppearance.html#//apple_ref/doc/uid/TP40006556-CH54-SW1), dp (density-independent pixels - see http://developer.android.com/guide/practices/screens_support.html#terms), "effective pixels" (see https://msdn.microsoft.com/library/windows/apps/dn958439.aspx#built-in_features_for_designers) or the like, with a note that whatever values you've chosen generally (though dependent on platform/OS/actual device/etc) will map to roughly 9 or 10 physical mm)
> 
> P
> -- 
> Patrick H. Lauke
> 
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Received on Thursday, 17 December 2015 21:34:01 UTC