Using Stan's statement that the resonant cavity operated at the "extremely low potential of 48 Volts", I was able to determine the resonant frequency. I set my Vernier calipers to 48 mm, then adjusted the screen size so the potential side of the resonance diagram matched. Then I measured the pulse rate side and it's 24 mm. So the resonant frequency, for his cavity, was 24 pulses per second. This two-to-one ratio doesn't hold for other voltages, due to the geometric relationship, but a similar method can be used to determine the ration at some other specific voltage.
