There isn't any need for the super accurate test rig. You can trade time
(pun intended) for money by using the U.S. Naval observatory clock on
the web to check the timekeeping accuracy over several days. In general,
we have always included a stored 'tuning' constant for long term timing
routines. The constant may need adjusting as the crystal ages. This is
generaly preferable to external adjustments.

Don't overlook line frequency as a good long term standard. Utilities
keep an awfully good average frequency so that there aren't any problems
with synchronization in the power grid.

-- Tom