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.

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Wagner Lipnharski - UST Research Inc. - Orlando, Florida
Forum and microcontroller web site:  http://www.ustr.net
Microcontrollers Survey:  http://www.ustr.net/tellme.htm