looks like there's a trend. The clock is moving to

Tomorrow 10am GMT I’ll fast forward the Trinity clock by 23 hrs for the end of Summer Time. watch in Great Court with tours up to see the clock mechanism. Coffee croissants in chapel. Why 23 hrs, not 11 hrs? I’ll explain tomorrow!. @Trinity1546 @TrinCollCam.

Join millions who have switched to Grok.

Coronation Chairleg - for King Charles's birthday.

Tomorrow morning, 10am GMT, I'll be fast forwarding the clock in Trinity College by 23 hours. This is instead of putting the clock back an hour. You might like to stand in a Great Court and watch the hands whizz around.

It's been a summer to forget. 25 June - 6 Aug only averaged 1006mbar (STP is 1013mbar). In 6 wks TC clock gained 2s. Oh no!.Why? Low air pressure = low density which decreases buoyancy of pendulum bob so apparent 'g' is more. Period=2π√(L/g) so clock goes faster. @TrinCollCam

And here's pressure measured on the train from London King's Cross to Cambridge. Slow pressure drop as altitude rises about 80m to Stevenage but the big dips are when the train goes through tunnels.

Amazed that I can measure the height of the clock tower with my phone. Barometric pressure varies with height. I had to unlock the door on the way up and on the way down. Hence the pause. This shows a height of 1.35mbar or 11.5 meters. Exactly right!

Some background to The Great Court Run is here - yes the idea is to run around Great Court (about 339 metres) in the time it takes for the clock to strike 12. Here is the run in 2012

5. Happy running!

4. Then there's air density. The spinning 'fly' controls speed by air drag and that depends on air density. It's clear then that the best chance of beating the bells is on a cold dry day 3 days after winding. /5

3. There is also the effect of weight of the cable so we can see that the strike goes steadily faster as more cable plays out, and then suddenly slower after 3 days when the cable goes down to a single layer on the drum. /4.

2. This is in part because of air density (tempreature/pressure/humidity) but the biggest effect is that the weight driving the bells runs onto a second layer on the drum which gives a bigger torque and therefore faster striking . /3

The Great Court Run is coming up. I've done an analysis over two years 2018-2020 and the time it takes to strike 12 averages 48 seconds but sometimes as slow as 46 seconds and as long as 50 seconds . /2

Thanks Sarah for driving so expertly! @TrinCollCam

Really lovely working with Sarah and Robero @TrinCollCam

Pigeons landing on the minute hand at quarter to the hour can stop the clock @TrinCollCam

Here is the pigeon wire close up @TrinCollCam It's very effective at keeping the pigeons off because they can't see their feet as they land

Thanks to Sarah and Robero for taking me up to the clock dial in a cherry picker to tighten up the pigeon wire on the minute hand. @TrinCollCam

Very pleased with this experiment to illuminate the clock dial @Trinity1546 @TrinCollCam

Tomorrow at noon I'll be ringing the bell in the clock tower of Trinity for 7 minutes, to mark the 7 days so far of the invasion of Ukraine.