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[css-d] understanding scaling factors for % and EM

Sent by Timothy J. Luoma on 30 September 2002 03:03


http://www.w3.org/TR/REC-CSS2/fonts.html#value-def-absolute-size 
recommends a 1.2 scaling factor for "absolute" font sizes, and suggests 
a base font size of 12.

Given that there are +3/-3 sizes
[ xx-small | x-small | small | medium | large | x-large | xx-large ]
I tried to make the calculations in PX, EM, and % but I don't think I'm 
doing it correctly (never been good at the math :-(

Here's what I came up with:

xx-large = 20.7px
  x-large = 17.3px
    large = 14.4px
   medium = 12px
    small = 10px
  x-small = 8.3px
xx-small = 6.94px

That seems pretty straight-forward.

What I can't seem to get through my cement-like cranium is how that 
transfers to EM and % sizes.

These are my calculations for EM:

xx-small = .58em
  x-small = .69em
    small = .83em
   medium = 1em
    large = 1.2em
  x-large = 1.44em
xx-large = 1.73em

xx-small = 57.8%
  x-small = 69%
    small = 83.3%
   medium = 100%
    large = 120%
  x-large = 144%
xx-large = 172.8%

Does any of this sound logical?  I seem to recall someone (Eric?) awhile 
back saying that EM is not exactly %, i.e. .8em ~= 80%

I'm trying to put this into practice at
http://tntluoma.com/css/tests/font-sizes.html

TjL

-- 
30 Days to becoming an Opera Lover
                                        http://www.tntluoma.com/switch
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