On 11/17/2011 8:18 AM, Bill Gill wrote:
On 11/16/2011 1:05 PM, nefletch wrote:
About 3 years ago, I bought a new Frigidaire microwave, and of course
it has
a digital clock on it. This crazy clock gains approximately a minute
every
2 months. Our stove right below it has a digital clock also, it keeps
perfect time. It's just maddening to look at both of them, and the
time is
always different. In this day and age, how is it possible that a digital
clock cannot keep time? just crazy


Quick calculation tells me that is about 1 second a day. Not
really a huge change, compared to many digital watches I
have owned. It could be better, but isn't really bad. The
biggest problem is that you have one on stove that is
probably synchronized with the power line frequency. The
power line frequency is (or has been until recently) very
accurately controlled so that the stove clock keeps
better time than the average quartz clock. Of course
the stove clock may need to be reset after a power
outage.

Bill

I would also think appliances, like microwaves and stoves, would sync to
the power line frequency, which has a good long term stability. If the
power line frequency average was off both the microwave and stove should
be off together. Might be interesting to use something like the clock in
a cell phone (which I presume is set by the cell provider and is high
accuracy) to see which clock is drifting (might be the stove).

Wouldn't think either clock would use a crystal oscillator, as in Jim's
post, but that would explain drift that shouldn't happen with power freq
sync. May be the best guess.