Dr Hulda worked along with her Son on many experiments to find the best way to destroy Parasites, Bacteria and Virus using a simple 30kHz frequency output delivering a 50% duty cycle, but with increased minimum voltage to 0.25V (this lowers amplitude) by adding R5 39K or 30K resistor.

Dr Hulda uses the term "positive offset" as a need for the zapper to work to destroy parasites and their eggs and larvae , therefore there should never be any "negative offset" in any zapper design. 

You can rest assured that ALL of our designs use the system Dr Hulda used, POSITIVE OFFSET SQUARE WAVE, with no possibility that the unit will produce any "negative offset" wave.