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Keeping Big Ben striking on time
>>Parliamentary clockmaker: I am another one of the clockmakers at the Palace of Westminster.
Not only do we come up here three times a week
to wind it,
three times a week we
have to do a time check.
And what we have to do, we have to phone up the Speaking Clock, take an accurate reading
on the stopwatch,
then go up and listen to the bells strike,so that's what I'm going to do now.
[Clockmaker picks up the telephone, rings the speaking clock, listens and replaces the telephone]
Now we have an accurate time reading. All we have to do now is compare it with the first
strike of Big Ben.
[Clockmaker leaves the room and climbs a staircase to the belfry]
What you're going to hear is, about twenty seconds to the hour, the quarter bells will
ring out sixteen notes,then there's a pause of about seven seconds and then the first
blow of Big Ben is actually the time signal, so we check to see how accurate we are.
We're allowed plus or minus two seconds.
[Big Ben starts striking]
>>Parliamentary clockmaker: Should be, shall we say three minutes, and we have got three minutes and twenty-one hundredths.
Now we've got the accurate time reading, what we do now is we enter it on to a log,
which has been going for about the last hundred years.
we put barometric pressure on the log, we put the temperature of the Clock Room,we make
a record of how many corrections and how much is actually on the pendulum, then we sign it
and put the date and the time on the log.Barometric pressure is 1016,
we put what time we did the time check (ten o'clock),
we sign it.
The temperature in the Clock Room is 64.
We have got nine pennies on the record, carry that over
and we just put it on the chart itself, that we're less than half a second slow.
How is the time adjusted if the clock is fast or slow?
>>Parliamentary clockmaker:This is an old English,
pre-decimal one penny piece that
we use to adjust the time.We have a little stack of coins on the pendulum shelf
and by placing one more penny on the pendulum, it speeds up the timekeeping
by two-fifths of a second
in 24 hours.This is how we can get it so accurate.
So, if I place one on, in 24 hours' time, it will be two-fifths of a second faster;
take one off, two-fifths of a second slower.
For more information about the Clock Tower and Big Ben, visit www.parliament.uk/bigben