Hi: Somehow I got dropped from the mailing list around March 9, but have been added back. Hi: I recently stumbled onto this at the Wiki page for tuning forks: https://en.wikipedia.org/wiki/Tuning_fork#In_clocks_and_watches Showing an NBS 1,000 CPS standard. related to a discussion on the GreenKeys list server about the history of the tones used for radio teletype. https://prc68.com/I/TuningForks.html#AFSK-Tones and that lead to the NBS 1927 Yearbook pages 40 and pdf page 408 https://prc68.com/I/TuningForks.html#NBS_1000_CPS_Standard https://www.google.com/books/edition/Standards_Yearbook/5h_9yYrnBCYC?hl=en&gbpv=0 Fig 16 (pdf pg 408) "Pendulum oscillations" and Fig 17 "Tuning-fork vibration". Can someone explain what's shown in Fig 16 on pdf page 408?  Maybe a Shortt pendulum can sitting on a shelf off the stack of bricks? -- Have Fun, Brooke Clarke https://www.PRC68.com axioms: 1. The extent to which you can fix or improve something will be limited by how well you understand how it works. 2. Everybody, with no exceptions, holds false beliefs.