William Sommerwerck wrote in message
...
Barring the possibility that your powerline frequency is erratic, I'm
inclined to accept Mr Cook's explanation -- that these clocks have poor
powerline filtering, and spikes get through to trip the counter. You might
try putting a ferrite choke on the line.

The LED clock has become uncommon, if only because it doesn't lend itself
to
cordless operation. I keep one in the bedroom for those occasions when I
need a loud alarm, but it's not atomically controlled.

This one looks interesting. It file://claims// to always display the
correct time
and adjust for DST -- which would require access to a stable time source.


http://www.amazon.com/Chaney-Instrum.../dp/B0000C0XPQ
/ref=sr_1_22?s=furniture&ie=UTF8&qid=1337435811&sr= 1-22

You might look for atomic clocks using vacuum-fluorescent displays.



This is an interesting monitor of UK mains frequency, especially when its
breaktime on commercial TV carrying football or some opium of the people
soap-opera
http://www.dynamicdemand.co.uk/grid.htm
But cycles summed over a day has to be spot on.
I want to know when the utility companies will give away "intelligent"
fridges rather than CFL , that only come on when this frequency is high

All the LED clocks I've ever had experience of always gain , never loose
time, maybe only a minute a quarter , but only gaining. So my assumption its
due to mains hash