[texhax] 1em after scaling/rounding

Uwe Lück uwe.lueck at web.de
Wed Nov 9 11:17:30 CET 2005

Some rather academic/numerical question
(to font experts like Karl Berry or experts in numerics like Alex Rozhenko):

According to TeXbook p. 433, 1em is 10pt with unscaled cmr10.
I am measuring by   \normalsize\setbox0\hbox to...{\hfil}\showthe\wd0.
This yields 1em = 1.00002 pt -- OK, a rounding error
that doesn't matter at all.

Now I load \documentclass[12pt]{article}.
I get 1em = 11.74988pt, i.e.: 11.75pt
-- to me this appears very different from which one would expect
By contrast:   \normalsize %% standard 10pt
   \@tempdima = 1em
   \multiply\@tempdima by 6
   \divide\@tempdima by 5
The final line yields 12pt -- when ignoring
the same absolute rounding error that 10pt produces.

... any ideas about 12.00002pt vs. 11.74988pt, i.e.,
12pt vs. 11.75pt!?


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