> So people's clocks read right.
> (There was a warning system for nuclear attack that worked when the US power
> grid switched to 50 Hz.)

Maybe it's just in case European terrorists strike and want to make US power
the same as in Europe? Imagine all those devices popping when they get a
taste of 230V, 50 Hz... better than any EMP :) (of course it doesn't kill
battery powered devices, but so what.)

Anyway, on the topic of the subject (but still off-topic of the list) :
At least here in Finland we have yet another stable time/frequency source;
the national broadcasting company (Yleisradio) apparently bases the line
frequency (15625 Hz) on a very accurate oscillator (Rubidium). So there's
a transmitter with lots of output power, easy to make an antenna for, etc.