[texhax] TeX Queries 4: Overfull boxes

[Joel C. Salomon]

On Wed, Aug 1, 2012 at 9:30 AM, Paul Stanley
<paulrichardstanley at gmail.com> wrote:
> Does the above depend on the size of the font? Presumably the physical width
> of em varies from font to font.

The size of the letter 'M' (the source of the term "em") does vary
from font to font. But the dimension known as an em is defined to be
the "size" of the font. E.g., whether the font is 12 pt Times Extended
or 12 pt Times Condensed, an em is 12 pt long; for 18pt CM, the em is
18 pt long; etc., etc.

That's not to say that the character called the "em dash" will be
exactly 1 em long; font designers can play all sorts of typographical
games. But TeX, when given lengths measured in ems, will use the size
of the font.

—Joel