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RE: px vs. pt

From: Todd Fahrner <fahrner@pobox.com>
Date: Thu, 27 Jul 2000 11:40:14 -0700
Message-Id: <v04220805b5a625651a70@[209.21.38.75]>
To: Rowland Shaw <Rowland.Shaw@seagatesoftware.com>, "'webmaster@richinstyle.com'" <webmaster@richinstyle.com>
Cc: www-style@w3.org
>  > > Under Win systems: Control panel -> Display properties -> Settings ->
>Font
>  > > size (small = 72 dpi screen res, large = 96dpi screen res)

This isn't so. Under Windows, small fonts = 96ppi logical res; large 
fonts = 120ppi. It's the Mac that has a traditional 72ppi logical 
res. All of these are quite likely to be wrong for most displays, 
which is one reason that points are not useful for screen use. If you 
feel compelled nevertheless to use points, make sure that no text 
works out to less than 9pt if you want it to be legible to many Mac 
users. It's not a question of the size of the characters on screen - 
they might be 10m high each -  it's that there will be insufficient 
pixels to draw upper- and lower-case roman text recognizably, without 
clogging up the counters.

I've got MacIE5 configured correctly to use a 115.5 ppi logical 
resolution (matching the actual physical res). My preferred font size 
is 14px (x-height: 7px) for this configuration. I can always tell the 
bozo sites using points immediately: they're the ones with the 
absurdly huge fonts. Like CNN, which sniffs my UA string, assumes 
that I don't/won't/can't/shouldn't configure my UA correctly, and 
proceeds to serve up "default compensated" CSS containing point 
units. And some that should know better, like XML.com. It's a good 
thing MacIE5's got text zoom; I have to reduce to 75% to read these 
sites unless I'm across the room.

In 20/20 hindsight, I think, absolute units should never have been 
made permissible for the screen media type, and pixels should have 
been permissible only on the root element (e.g., HTML). This way 
users could override the value on the root element as necessary in 
user stylesheets to scale all relatively-sized children (including 
raster art), without having to depend on the rare good sense of 
implementors to provide magic (non-CSS-based) UI stuff like Zooming. 
(Assuming inheritance worked into, e.g., table elements, which it 
doesn't in the leading implementations, and that non-CSS-based 
presentation prefs UI were formally deprecated, with user CSS UI 
becoming a conformance requirement. But 1996's technopolitical 
climate would not have permitted such a saving degree of 
specification for CSS-1.)
--
Todd Fahrner
Web UI Technologist
Metrius
Received on Thursday, 27 July 2000 14:42:16 GMT

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