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[css3-values] unit equivalence (was: [CSS21] response to issue 140b)

From: Ernest Cline <ernestcline@mindspring.com>
Date: Fri, 13 Feb 2004 00:29:38 -0500
Message-ID: <410-22004251352938593@mindspring.com>
To: "W3C CSS List" <www-style@w3.org>




> [Original Message]
> From: Bert Bos <bert@w3.org>
> To: fantasai <fantasai@escape.com>
>
> This is the CSS WG's response to an issue you raised on the last CSS
> 2.1 draft (http://www.w3.org/TR/2003/WD-CSS21-20030915). 
>
> Your e-mail:
>
>     Is the computed value of "1cm" and "10mm" the same or different?
>     Because you need to convert in order to make them the same, and
>     converting units involves computation...
>
> CSS WG response:
>     We appreciate your input but we don't really want to change this
>     at this time.

Actually, I would have to say that in the context of CSS, it would
be best to not require that 1cm = 10mm exactly.  Here's why:
The UA may wish to use a non metric value for its internal use.
Now if 1cm is converted  to x units and 1 mm is converted  to y units,
it need not be the case that x=10y when both conversions are done
to the best ability of the device. Even if x=10y, given the effect of
round-off error, it might well be the case that 1.3 cm would not be the
same as 13mm for the same reasons that 1.3 * 10 might not equal
13 on a binary computer.

As for whether CSS 2.1 should mention this, probably not,
but the WG should think about including a note about this in
CSS3 Values and Units.
Received on Friday, 13 February 2004 00:29:32 GMT

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