> How about the really, REALLY obvious one?  The units used by TeX?
> Used successfuly on everything from 16-bit 640k DOS to supercomputers
> and useful for a wide range of output devices, yet fitting within a
> reasonable range of integers.

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 ;-)

Cheers,
  - Andreas

[*] TSQOTD: The Stupid Question Of The Day