Great Clock adjustments
25 August 2015 (updated on 25 August 2015)
Clock mechanics first became aware of a slight delay to the Great Clock on the weekend of 15 August. The clock was checked, and it was confirmed that it was late by approximately 6 seconds. This delay was corrected by the clock mechanics, who brought the clock back to within normal parameters (striking within less than 2 seconds of the correct time).
Parliament’s clock makers have been closely inspecting the different parts of the clock, and are still monitoring it to find out what caused the loss of time. It may be that several small problems contributed to this unusual problem, and at present the mechanics are particularly observing the pendulum, air pressure and temperature, the escapement mechanism and the gears.
Today, the Great Clock is accurate to less than one second. This was ensured by regularly checking the time, and adjusting the number of old penny coins that are used as weights to reduce the length of the pendulum and increase the rate of swing. Adding or removing each penny changes the clock speed by 0.4 seconds per day.
The clock mechanics will continue to monitor the performance of the clock, and have increased their routine checks from three times per week to every day, including weekends.
Further information
- Living Heritage: Big Ben
- Facebook: Big Ben Q&A with Ian Westworth [5 August 2014]