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Re: Sizing

From: David Woolley <david@djwhome.demon.co.uk>
Date: Sun, 17 Sep 2006 14:21:11 +0100 (BST)
Message-Id: <200609171321.k8HDLBo03731@djwhome.demon.co.uk>
To: www-style@w3.org

> What is rendered on screen always varies depending on the screen resolution.
> Units like "pt" are never displayed in their correct sizes. Similar for

That's a platform problem, and may not even be a browser problem.  Only
if the platform knows the display size can it correctly calculate this and,
providing correct display size information is generally beyond the capabilities
of the average Windows user.

In the case of projection devices, the problem may be particularly 

> printing: "px" unit rules are never printed in the printer's resolution.

px are rather funny units, but I think the basic design principle is that
they should be an integral multiple of the device pixel and that ratio
should be one for typical 1999 CRT display and video card combinations.
Designing in pixel sizes is generally a bad idea for a language like
HTML which is intended to be usable on an extremely wide range of devices,
details of which are not known to the author.

If px sizes were used literally on printers, the result would be images 
that were maybe 10 times smaller than on the computer display (120 dpi
display, versus 1200 dpi printer).  They might also have strange aspect
ratios, as some printers may have rectangular pixels.

>          "300pt" => 300 pixels equal one Point
>          "500cm" => 500 pixels equal one Centimeter

The author doesn't have access to this information.  But in any case
72pt = 2.54cm by definition, so pt:px and cm:px cannot be defined
Received on Sunday, 17 September 2006 13:21:16 UTC

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