> understanding is the 60Hz line in the US / Canada is spot on, and
> I imagine the 50Hz throughout Europe is likely just as stable

In most developed countries the national grid is well-regulated and
providers would have to have comply. Note that this doesn't
necessarily mean they have to stick to exactly 50Hz or 60Hz, but
that they are required to generate a certain number of cycles per
day

For example, during peak periods (eg 8-9am, 5-6pm) the frequency
would possibly drop to 49.something and in off-peak (overnight) the
frequency will rise to 50.something

Therefore it is possible for a mains-derived clock to be inaccurate
for much of the day but overall, comparing day-to-day measurements,
has good repeatability

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist