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David Pike wrote:

> How do they get a 12hr 25 minutes revolution. 

I think they simply use a Quartz Crystal tuning fork that is cut to oscillate at (2^15 / 1.035046 (Hz) ) so then, they can use the same electronics divider and the same set of plastic gears as is used on a standard 12 Hr clock David. To test this, I counted 60 "ticks" of my tide clocks, and it took 62 seconds (60 x 1.035046) of time - using the "time.gov" digital clock on my phone.

If you carefully time Moonrise for 40,000 days in a row David, you should end up with a nice graph that looks like this.

> To be strictly accurate should I have used  29° to the hour?

Yes, I agree with the 29, but a much greater error is how much the "actual tide" deviates from the simple use of "just" the M2 harmonic constant of the Moon that rotates around the world at a speed of 28.984104 (degrees per hour).

David, you might like to have a read of a little piece I wrote back in 2020 - "How do you set a Tide Clock ?"

> Finally, why do you think I accidentally on purpose dropped a spot of white paint on the black clock caps?

      If it is like my Tide clocks David, the top most central spindle is the shaft for the "seconds hand", so I imagine your white dot goes around once every 62 seconds to indicate the battery is not flat - a sign of life indicator perhaps.

      Regards, Geoff Hitchcox, Christchurch, New Zealand.