For independent standards (not quite what you asked) I recall from "The Science of Clocks and Watches" (a book with much technical info if you're interested in these mechanical devices) that the most accurate mechanical/pendulum clock was the Shortt Clock that used a pendulum in a vacuum chamber for its standard. Mechanical clocks were replaced by more stable electronic quartz crystal oscillators, and then finally by atomic clocks.
Perhaps closer to your question: I recall in my readings about clockmaker John Harrison (likely either in "The Quest for Longitude" or Dava Sobel's "Longitude") that he would look from the edge of his window at a particular star each night and note (while counting the ticks he heard from his clock) the exact moment it would disappear behind a nearby chimney, and knowing the Earth's rotation takes four minutes and some (I forget) seconds off from a day, he used this to calibrate and test the precision and accuracy of his long clocks. It was suggested he could get within less than second with this method. This was around age 21, so the year would be about 1714. Looking online for PZT (photographic zenith tube), I didn't find much about it, but it was surely first made a couple centuries after this. The Sobel book (all about how Harrison won the Longitude prize) is more a popular book and less technical, but "Quest" has many mostly-technical articles, mostly about Harrison, as well as beautiful photos of his clocks. One or two of the articles is by the man who made (or made the parts for it, the story is complicated) the one-second-in-100-days "Clock B" pendulum clock, built from Harrison's writings and claims of just that accuracy in the book he wrote shortly before his death. On Mon, Mar 25, 2019 at 7:00 PM John Ackermann N8UR <j...@febo.com> wrote: > > Does anyone have a pointer to information about the absolute time > accuracy (not stability) that was available via PZT or other techniques > prior to the Cesium definition? I'm doing a presentation and want to > show the evolution of accuracy. My Google-fu has failed me in finding > anything pre-Atomic. > > Thanks! > John > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.