I have here the Apidictor diagram Tom sent along with a leaflet by Rex Boys, but thorough analysis of the Apidictor circuit gives but a rough idea what sound pressure impinging upon the microphone caused a transition from the green zone to the yellow zone, and from the yellow to the red. There are many unknowns in the equation, such as the sensitivity of the microphone used, and more variables inside the instrument. These days one might use a meter as intended in Mark 5 Apidictor, or even green, yellow, and red lights, but in any case, the indicator of choice must be calibrated. What we lack is knowledge of what accoustical levels in the frequency band of interest correspond to the various degrees of imminence of swarming. Without that knowledge it may be necessary to reestablish the calibration criteria empirically, as Eddie Woods originally must have done. Testing of an extant Apidictor could yield calibration data, which could help the effort to resurrect the instrument in modern form. Hope this clarifies what piece of the puzzle is missing. If anyone can provide such data, it would be most helpful. Bill Morong