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Only a few years ago the clock on my microwave oven never needed
adjustment except for daylight saving time changes and the occasional
power failure. That's no longer the case. An article at the NIST site
explains.

"Due to the efforts of Henry Warren, inventor of the Telechron electric
clock, electric power companies have been a source of time and frequency
reference for the public for over a hundred years. However, advances in
technology and changes in the electric power industry have generated a
movement within the industry to end the time-reference service. Power
systems in the U.S. operate at a nominal 60 Hz, but in actual operation
they accumulate significant phase error. It must be deliberately backed
out to keep synchronous clocks on time--a procedure known as Time Error
Correction (TEC). Today, many electric clocks still depend on the power
system as the reference oscillator--that is, are synchronous--while
others use other time references, such as local quartz oscillators and
networked time servers--a benefit of the Internet of Things. Little is
known about the overall impact of TEC on timekeeping in modern times.
The Blackout of 2003 spawned a new regulatory structure for the electric
power industry to improve reliability, and as an unanticipated side
effect, a decision process that would most likely eliminate TECs was set
in motion. The specific proposal is to retire regulatory standards
designated BAL-004 and WEQ-006. We review the relevant structure and
governing bodies of the U.S. power grids, and report on the current
procedural status of these standards. In addition, we review possible
scenarios for the future of the power system as an elapsed-time
reference absent TEC. For this, we include analysis of the electric
power at USNO, as measured over five years. The TECs appear in the data;
an analysis with the industry-supplied record of the TECs indicates that
without them a time deviation of about 7 1/2 minutes would have occurred
on the Eastern Interconnection (grid) between the daylight saving time
switches of March 2016 and November 2016."

https://www.nist.gov/publications/time-and-frequency-electrical-power-lines

   

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