Original poster: "Mccauley, Daniel H" <daniel.h.mccauley-at-lmco-dot-com> I believe this is similar to the Gaseous Tube testers (handheld) that you see. Basically, a small tesla like system inside of the unit. You adjust the voltage and arc by adjusting the gap distance of the spark gap. Dan > Is it an X-Ray transformer? Is it an Ignition Coil? Or What? > > Curious in NJ > > KL > > >