gEDA-user: Using 60Hz mains frequency for timing?

[Randall Nortman]

Just a quick non-gEDA design question -- I have the choice between
using the zero crossings of the 60Hz mains voltage or my MCU clock
(generated from an 18.432MHz quartz crystal producing a 48MHz CPU
clock via PLL built into the MCU) for low-resolution timing.  The
crystal is not designed as a watch crystal, so its tolerance is
probably pretty poor, and furthermore this board will see wide
temperature swings, which I think has an affect on the crystal
frequency as well.  I have no idea how precise the 60Hz line frequency
from the power utility is, but it at least is probably not
temperature-dependant.  Either one is easy to use -- I just want to be
as accurate as possible.

Anybody have suggestions?  TIA,

-- 
Randall