Re: OFFTOPIC: Font Metrics and Typographic Units

From: John Cowan (
Date: Thu Jan 14 1999 - 12:34:18 EST

I already sent this to the author, but since there has been
a follow-up (on metric font sizes), I thought others might
want the current facts.

The inch has by international agreement (US, UK, maybe others) been
exactly 2.54 cm since 1959. The "U.S. survey inch", which is
used for official government survey maps, is still 1/0.3937 cm, but
this is a very special purpose unit.

The printer's point was defined in 1886 by the American Typefounder's
Association to be exactly .013837 in, which by the current
definition of the inch would be exactly 3.514598 mm. The
TeX definition of the point, 1/72.27 in, is slightly larger: one
"classical" point is .99999999 TeX points. The difference between
these two points is only about 0.3 nanometers. Even if you are doing
chip lithography, this should make no difference to you!

Furthermore, the Postscript definition, 1/72 in, is only about
52 micrometers larger than the TeX one. Again, this is hardly
likely to be a problem in practice.

John Cowan
	You tollerday donsk?  N.  You tolkatiff scowegian?  Nn.
	You spigotty anglease?  Nnn.  You phonio saxo?  Nnnn.
		Clear all so!  'Tis a Jute.... (Finnegans Wake 16.5)

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