Precision Pendulum Clocks, Gravity and Tides

*16-Nov-2009*, updated *08-Dec-2021*

Below is a series of articles I wrote while exploring the relationship
between **pendulum clocks** and **gravity**,
specifically what happens to the timekeeping performance of
high-precision pendulum clocks
as gravity changes due to **tides**.
We all know about ocean tides and how they are somehow caused by the
motion of the earth, sun, and moon.
We also all know that pendulum clocks swing back and forth based on
the length of the pendulum rod and earth's acceleration of gravity.

But it is less well known, but perhaps now obvious, that the period of a pendulum clock varies ever so slightly as the earth's acceleration of gravity itself changes due to the periodic influence of lunar/solar tides. This effect is so small, however, that only the very best, laboratory-grade, vacuum-sealed pendulum clocks can "see" the effect. All other mechanical clocks are too inaccurate for tides to make any practical difference.

So in the long history of precision pendulum clocks, "seeing tides" has become a sort of prize. If your home-made precision pendulum clock can detect tides, it must be exceedingly accurate. This series of articles explores topics of tides, gravity, pendulum clocks, accuracy, stability, comparisons of the very best pendulum clocks ever made (such as Shortt, Fedchenko, Littlemore), and a search for why some pendulum clocks that should have detected tides didn't.

- [01/2006] Lunar/Solar Tides and Pendulum Clocks (part 1)
- [09/2008] A Shortt Lesson in Allan Deviation (Tides, part 2)
- [11/2009] A
*Dream*Pendulum Clock (Tides, part 3) - [11/2009] What Changes When Gravity Changes (Tides, part 4)
- [01/2012] Understanding Hybrid Quartz / Pendulum Clocks
- [09/2013] Fedchenko: Clock or Gravimeter? (Tides, part 5)
- [10/2013] A New and Wonderful Pendulum Period Equation
- [01/2014] Pendulum Simulation 1: Period and Circular Error
- [12/2014] Pendulum Simulation 2: Changing Length or Gravity
- [02/2015] Digital Compensation and Pendulum Clocks
- [04/2015] Pendulum Accuracy, part 1 - Purity and Quality
- [12/2021] Spectral Analysis of Pendulum clocks (Tides, part 6)

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