David Looser wrote:

What was noticeable was just how fast mains frequency variations can occur.
Frequency variations of the order of 0.1% can occur in a matter of seconds,
an 0.5% variation within a minute or two.

http://www.nationalgrid.com/uk/Elect...ncy/Freq60.htm

When would be the correct time of the day to make perfect speed
recordings from my synchronous motor powered record deck?


I'm sure that the pattern of this
sort of variation does not conform to a pattern, but is unique on each
occasion.

It's related to the current appalling state of the weather and what's
just been suffered through on TV ...

--
Adrian C