evidence: How does zapping work? Dr. Clark has written, "Any positively offset frequency kills all bacteria, viruses and parasites simultaneously given sufficient voltage (5 to 10 volts), duration (seven minutes), and frequency (anything from 10 Hz to 500,000 Hz)" [2]. A positive offset frequency is one which alternates between positive and zero voltage. I am not at all certain that zapping actually kills any invading microorganism. This trial suggests that since only 48.3% improved substantially, zapping probably did not kill "all bacteria, viruses and parasites" (according to Dr. Clark's book, the reason could be that possibly the current did not access all body regions, specifically the bowel contents [2]).