While many things affect a quartz oscillator in your watch, the secret
to its great time keeping is the fact that when the watch is on your
wrist it is kept at a very stable temperature (~97F). As long as you
wear the watch, the oscillator will remain stable and drift hardly at
all. Put the watch in an environment where there is significant
temperature swings (such as your car) and you will see the accuracy
degrade quickly.

This same reason is why computer clocks are off so much...the machine
is on and off enough that the temperature the oscillator see changes
significantly.

While I have not seen the time keeping circuitry of a SUN station, I
would wager that they had a small oven for the oscillator that kept the
quartz crystal at a stable temperature.

While the accuracy of a timepiece is impressive, what also impresses me
is the extreme low power requirement that allow the circuit to run for
years on almost no power. Part of that is because of the LOW
(microamps) current requirements and the low frequency (~32KHz) of the
oscillator.

Amazing what technology one can buy for a few dollars...we really don't
appreciate the technology that is all around us.

TMT