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

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 20:47:36 UTC