I have the Dynon converters, too, but haven't tested them yet.
One way to play with them is to put a test load on them and measure the output voltage. Rzbill quotes 180 pF empty, 360 pF full (plus/minus some biases from the tank connector to cap plates)
An easy tank simulator would be a length of RG-58 coax, which has a capacitance of about 30 pF/foot. Crimp on a connector on one end and connect to the Dynon gauge. 12 ft would give you a "full" tank, 6 would give you an "empty" tank. Simply trim the end to adjust the capacitance (just cut it with a wire cutter; be sure the shield and center conductor don't short when done).
I'll go do this and report back ...