In message
"Dave Plowman (News)" wrote:

... would counting 2,592,000 AC zero crosses do the trick?

In the UK, the mains frequency might well average out at 50 Hz over 24
hours, but that's not the same as being absolutely accurate over any 6
hour period.

I've a radio-controlled clock and a nominally-50Hz-driven one in the
same room.
There's only any point in synchronising them early in the morning: that
way, they'll agree again every morning, i.e. the 50HZ is carefully kept
to be *on average* true, but by evening, especially in winter, the
difference can be as much as 20 seconds.

Can't see the US being any different.

Nor can I ...

--
Peter Duck