>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.
>

  Wagner:

  It all depends on your time scale. If it's on the order of seconds,
  the crystal is probably better. If it's on the order of days, the
  power line is probably better. If it's in between, more info is needed.

  Measuring the accuracy of the power line over time is like measuring
  the accuracy of your car's position over the length of a trip. If
  you're only going a couple of miles, At any one time your position
  could deviate from the desired position by a few yards. If you're
  only going a couple of miles, the percentage accuracy is not great.
  If you're driving across the country, a couple of yards at your final
  destination is still pretty good accuracy. With care, your final
  position could be within a few ppm of the desired one.

  Regards,
  Reg Neale