The pendulum clock in Trinity College, Cambridge was installed in 1910. It is remarkably accurate, known to be better than one second per month. In 2009 a system was installed to monitor the "going". The work was done as part of a 4th year MEng project at the Engineering Department. A sensor on the pendulum detects the going of the clock, which is compared to the accurate time signal from a GPS receiver.

Here is a graph for the last 30 days of drift (updated every 3 hours):

For an entirely mechanical clock the accuracy is remarkable.

A barometric compensator was installed at clock change - midnight 28 March 2010.

The clock is regulated as infrequently as possible so as to stay within +/- 5 seconds of the correct time. This enables the steady-state physics of the clock to be examined without unnecessary interference.

The black dots ● indicate that there is a comment relating to the time indicated. Blue arrows pointing down indicate that an adjustment was made to the Going of the clock by removing weights from the pendulum. Red arrows up indicate addition of weights to speed the clock up.

Comments (see all | edit)

14 Apr 2014 [22:01]
ADJUST: +300 ms/day to 39800
14 Apr 2014 [22:00]
found the computer dead due to power surge earlier in the day. Did a topup wind with Ben Moss @B_R_Moss, after seeing the amazing ISS passby.
14 Apr 2014 [14:00]
Brownout, and the computer has died. No data for a while....
13 Apr 2014 [16:08]
Hector Senior, Elishna ODonovan, Glencora Senior, Elizabeth Senior and Imre Leader all wound very deftly - and we corrected the quarters that were out of sync.
09 Apr 2014 [15:51]
winding by Alessendro Cabboi, Alice Cicirello (>2*pi) and Hilary Costello - many thanks!
02 Apr 2014 [16:40]
ADJUST: -270 ms/day to 39500 and a top-up wind assisted by Rachel Greene, the new College chaplain
01 Apr 2014 [14:45]
I have hung a white sheet in the window to diffuse the sunlight that shines strongly onto the pendulum and mechanism in the afternoons. I hope this will reduce the extremes of temperature and will calm down the fluctuations in going. Also did some winding.
30 Mar 2014 [00:02]
ADJUST: -30 ms/day to 39770, clock change for summer time and winding assisted by Anne Bahnweg, Augustine Mzumara @ThisIsGus and Christopher Hicks - big decision to set the clock for the next seven months. Follow it on @clockkeeper
28 Mar 2014 [15:41]
ADJUST: -5600 ms/day to 39800 followed by a restart of the computer and updating the National Instruments drivers. A bit of a bother. Would rather set this computer up to use the sound card.
28 Mar 2014 [13:56]
Here is a good check that adding the 5000ms/day weight does what it says, speeds the clock up by 5000 ms per day [link] and given that all the weights are scaled in proportion to mass the set we have looks pretty good
28 Mar 2014 [12:20]
ADJUST: +5000 ms/day to 45400 in readiness for clock change tomorrow night, I want to start the new season off near zero so that we can test the barometric compensator.
24 Mar 2014 [20:00]
ADJUST: -300 ms/day to 40400
24 Mar 2014 [19:55]
Twenty cubs did the winding tonight! Thanks to 12th Cambridge Cubs and their leaders. Cubs were Jude, Rebekah, Benji, Harry, Chiara, Eleanor, Timoni, Tomas, Lucas, Alex, Gregor, Henry, Jamie, Bill, Rory, Tom, Johnny, Oliver, Reith, Archie with leaders Jane, Mark and Arusha
24 Mar 2014 [09:51]
ADJUST: 4900 ms/day to 40700 after installation of further weights to the barometric compensator. 240g was added to each side, totalling 480g added. This should improve the accuracy of compensation. We shall see ...