This post was written by Andrew Strangeway

As a clockmaker, or practising horologist, there is one particular moment while waiting for a clock to strike when time seems to slow down.This moment is more daunting when the streets outside are lined with 100,000 people and millions more are watching live on television, and streaming, waiting to hear the clock chime.

On December 31st it all comes down to a single moment, when the nation watches and waits for Big Ben to ring out and signal the start of the new year. Behind the scenes, however, months of preparation go into ensuring that this first hammer-blow falls precisely on time. Besides the installation of additional broadcast equipment, regular servicing, and thrice weekly winding there is also timekeeping: ensuring, literally, that the clock stays on time.

In the months leading up to the end of 2023, the timekeeping of the Great Clock was a core focus. After the break of six years during the servicing of the clock and tower, the twice-daily live chimes finally returned to BBC radio airwaves on November 6th. This New Year marked the 100th anniversary since the bells were first broadcast live for New Year’s Eve. It was a matter of pride that the clock should perform well and strike on time.

When it was first installed, the Great Clock was, by some margin, one of the most accurate public clocks in the world. The original specification for the clock set down in 1846 by George Airy, the Astronomer Royal, required that ‘the striking machinery be so arranged that the first blow for each hour shall be accurate to a second of time’. As clockmakers our job is to ensure that the clock remains true to this original purpose. To our advantage, we have highly accurate timekeepers to compare the Great Clock against and, armed with this information, we can regulate the pendulum carefully and actually comfortably exceed the original target for accuracy.

Since starting at the Palace of Westminster in August 2023, I have implemented the use of a new custom-made timer to increase the accuracy of the timing of the first hammer-blow of the hour and an improved regimen of regulating the rate of the clock’s pendulum. The core mechanics of regulation remains as ever: the placing or removing of weights, in the form of old currency, on a small platform partway down the length of the pendulum rod. Famously, one pre-decimal penny added speeds up the clock by about 2/5th of a second over 24 hours. These are a little too weighty and the adjustment too coarse if one is aiming for a finer degree of accuracy. I have begun using ha’pennies and farthings for regulation, kindly lent for the purpose by my colleague in the clock team, Ian Westworth. These speed the clock up by about a quarter of a second a day and a tenth of a second a day respectively.

In the final days running up to New Year’s Eve I was at the top of the tower, on the hour, throughout the day to take a timing reading from the strike and to make small adjustments to bring the clock precisely to time. As luck would have it, on the evening of the 30th we experienced heavy winds, which buffeted the tower and were enough to throw the clock out by 0.2 seconds by the morning of New Year’s Eve. I was able to correct for this by the evening. Midnight came and Big Ben struck, and the view of the fireworks from the top of the Elizabeth Tower was astounding. It was awesome to see the fireworks perfectly synchronised with the strike of the bell.

My timekeeping efforts were rewarded when we measured the timing of the strike from the sound recording compared with a GPS clock – these results were generously provided by Mark Powell of DeltaLive. The result was that Big Ben struck midnight at exactly 23:59:59.981, within less than a fiftieth of a second of midnight. That’s less than a fifth of the time it takes to blink your eyes. I must confess to being rather pleased with that!