I wonder how the power grid keeps phase sync adjusting the frequency, or
worst, the phase, between each other power plant only few times a day. 
In Brazil they have a huge power grid "on very tied sync" at the south,
including the world largest hydroelectric Itaipœ plant. One plant can
not have its phase out of sync, or the grid starts to fall down and a
complete blackout happens. I am not an expert on this, so I may be wrong
about how they do it.
Wagner.

Dave VanHorn wrote:
> 
> > Does anyone already did any research about what is more accurate to get
> > 1Hz division; the 60Hz power line frequency or a cheap 32768Hz crystal?
> > The fast answer could lead to the crystal, but it could not be the
> > truth.  I have an "old red led display table clock" that steals clock
> > from the 60Hz power, I never needed to adjust its timming error (it was
> > never noticed) except for day-light-savings adjustments.  Dallas RTC
> > DS-1644 has almost one minute/month error with an internal crystal.
> 
> You won't see any long-term problems on the power line other than missing
> cycles.
> They adjust the power frequency to keep in sync with atomic clocks. It used
> to be done manually, a very fine vernier, it's probably now under computer
> control. For the best of all worlds, use your own osc or internal counter,
> and re-sync to the power line periodically.