"Andreas Raab" <andreas.raab at gmx.de> wrote in reply to
my suggestion of using TeX's internal unit:
	Okay, that's probably TSQOTD[*] but what exactly _are_ the units
	used by TeX internally?  I at least have no idea whatsoever as
	I've never had the need to think about how TeX represents my
	real world units internally ;-)
	
Scaled points:  65536sp = 1pt = (1/72.27)in = 0.35146mm
1sp = 5.36285um.

Chosen so that a fairly wide range of units (including bp = Postscript
points = (1/72)in approx= 65782sp) could be manipulated in binary
arithmetic without too much error.