The Shortt clock, made in the 1920s, is the most famous accurate clock pendulum ever known, having an accuracy of one second per year when kept at nearly constant temperature. Almost all of a pendulum clock's accuracy resides in its pendulum. If the pendulum is accurate, the clock will be accurate. In this book, the author describes many scientific aspects of pendulum design and operation in simple terms with experimental data, and little mathematics. It has been written, looking at all the different parts and aspects of the pendulum in great detail, chapter by chapter, reflecting the degree of attention necessary for making a pendulum run accurately. The topics covered include the dimensional stability of different pendulum materials, good and poor suspension spring designs, the design of mechanical joints and clamps, effect of quartz on accuracy, temperature compensation, air drag of different bob shapes and making a sinusoidal electromagnetic drive. One whole chapter is devoted to simple ways of improving the accuracy of ordinary low-cost pendulum clocks, which have a different construction compared to the more expensive designs of substantially well-made ones. This book will prove invaluable to anyone who wants to know how to make a more accurate pendulum or pendulum clock.

General 1. Better accuracy from simple pendulums 2. A short history of temperature compensation 3. Scaling the size of a pendulum 4. Finding a pendulum's axis of rotation 5. Does a pendulum's axis of rotation shift with amplitude? 6. Some practical properties of quartz 7. Putting Q in perspective 8. The Allan variance and the root mean square time error 9. Transient temperature effects in a pendulum 10. Transient response of a pendulum to temperature change 11. Dimensional stability of pendulum materials 12. Variations on a Riefler bob shape 13. Bob shape 14. Rate adjustment mechanisms Suspension spring 15. Spring suspensions for accurate pendulums 16. James' suspension spring equations 17. Barometric compensation with a crossed spring suspension? 18. Solid one-piece suspension springs 19. Stable connections to a suspension spring 20. Stability of suspension spring materials Pendulum rod 21. Pendulum rod materials 22. The heat treatment of invar 23. The instability of invar 24. Position sensitivity along the pendulum rod 25. Fasteners for quartz pendulum rods 26. Effect of the pendulum rod on Q Air and clock case effects 27. Correcting the pendulum's air pressure error 28. Pendulum air movement: a failed experiment 29. Pendulum air movement: a second try 30. Time error due to air pressure variations 31. Effect of the clock case walls on a pendulum Electronics 32. An electronically driven pendulum 33. Sinusoidal drive of a pendulum 34. Photoelectronics for pendulums 35. Check your clock against WWV 36. Electronic correction for air pressure variations

Robert J. Matthys , Former Senior Research Engineer, Honeywell Inc, Minneapolis, MN, USA