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The Natural Philosopher[_2_]

wrote:
On 9 Mar,
Chris J Dixon wrote:

Dave Liquorice wrote:

Oh they do! Questions get asked in the house if they don't. IIRC the
last time they had to announce that mains driven clocks had the wrong
time and would need to be corrected was during the winter of 1947...
Back in the late 60s, I spent some time at Eggborough power
station. There was an interesting clock on the wall of the
control room. It clearly had two inputs - one was from the
station mains frequency which was driving its second hand (can't
remember if there were actually any others) forward, whilst it
was driven backwards by the station instrumentation feed, from a
pendulum clock which produced pulses ever second (and minute,
quarter hour etc for various printing recorders).

So the hand moved around the dial, twitching back every second,
generally hovered around 12 o'clock, but did move around a little
over time.

Mains driven clocks are allowed to drift off by so many seconds a day. Before
privatisation it was kept very close to zero, but needed to catch up (or
even anticipate future slow running) at night. Since then the full range of
drift has been more likely to occur. If memory serves (probably not) the
legal requirement was about 30 seconds.

The clock will have been to show the difference. We had seperate clocks at
work which showed the difference.

That's short term. I believe that over a day, the grid has to average to
spot on.

The shortfall is generally made up at night when demand is low, and all
the pumped storage has been replenished.