It'll vary as the cell drops emf. That's why a modern alkaline cell is prefer to a carbon zinc in these things. Fwiw, think of this as a slo-mo Accutron with a balance wheel instead of a tuning fork, otherwise almost identical. An even slower slo-mo version is the Kundo Electronic pendulum clocks, virtually identical to the Accutron tuning fork timepieces.I'm not super worried about mine. I used an (admittedly uncalibrated) CD-V700 geiger counter to check the markings on my Golden Hour, and though the meter shows a fair amount of deflection with the probe right near the clock with the 'beta shield' open, it shows much less with it closed, and next to nothing when I pull the probe a few feet away. Also, later examples (post-1965 or so) Golden Hours were produced without radium paint, according to this page, so you don't have to worry about all of these clocks.
I knew that was the rate adjustment; I just had no idea exactly how far out from 'normal' it was. I also wasn't sure exactly which direction you turned the screw in order to make it go faster or slower. After some experimentation, I'm pretty sure I've got it down pat at this point, and it's fairly close to accurate.
-Adam
http://sound.whsites.net/clocks/kundo.html
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