We get a lot of questions about complicated zappers with variable frequencies. Here is the answer in Hulda Clark’s own words:
“Many variations in zapping technique have been discovered since the first one found around 1990.
“The original technique showed that very small animals, like our parasites, could be killed with a very small voltage. But only IF the voltage is 100% Positive offset and only IF the voltage is varied up and down repeatedly.
“If the varying voltage becomes NEGATIVE, even momentarily, it supports and maintains their lives! This must be avoided. You cannot take this for granted when you purchase a Zapper. The maker must assure you that it has been checked on an oscilloscope and not even the briefest spike of Negative voltage found…
“If the voltage is applied in pulses, to produce a ‘square’ wave, it will affect many parasites at once so that the rate of pulsing, called frequency, is not critical. Even though these tiny animals undoubtedly have a ‘mortal frequency’ (a frequency that kills), this rate does not need to be known or used when a square wave of electricity, totally Positive, is used.
“A Positive electrical force that pulses up and down not only appears to kill tiny invaders; it also seems to energize your white blood cells to go on an all-out attack on your enemies: your parasites, your toxins, your bacteria, everything.”
– Hulda Clark
“The Cure and Prevention of All Cancers,” page 159

Nikola Tesla: Frequency Therapy Pioneer
During the early 1900’s Nikola Tesla was experimenting with all things electric including Radio Frequency. While researching radio waves he noted several assistants reporting that exposure to high frequency was healing their infections, wounds, and other ailments. Tesla was intrigued by such a thought, and brought the concept to several other scientists of his time for further research.
Georges Lakhovsky, Royal Raymond Rife, Albert Abrams, Wilhelm Reich, Bob Beck, and Hulda Clark all owe Nikola Tesla their beginnings.