Hi guys, I made a couple theremin calculators using Wolfram Alpha. I hope they might be useful to some.
These calculations come from 'Physics of the Theremin' by Skeldon et. al. (1998)
Antenna Capacitance http://www.wolframalpha.com/widgets/view.jsp?id=172d910bd9c5614bdbdcfd6b72d86982
Change in Antenna Capacitance due to Hand Proximity http://www.wolframalpha.com/widgets/view.jsp?id=e4c7f6eeec73e6d2404cc030a150470c