In her books the American biophysicist and physiologist Dr. Hulda Clark assumed a connection between parasite load and sometimes severe and persistent diseases.

Hulda Regehr Clark (1928-2009) with a doctorate in physiology developed a test device, the so-called synchrometer. By means of resonance reaction to specific frequencies the synchrometer was designed to detect pollutants accumulated in the body from industrially processed food, cosmetics and other products of everyday use, as well as various parasites, bacteria, viruses and fungi, which, according to her theory can (supported by the pollutants accumulated in the body) settle in the organs and cause serious chronic diseases. According to her theory, the pollutants, parasites or bacteria "reveal themselves" through a measurable resonance reaction to "their" specific frequency. So they can be weakened by fine electrical stimulation at precisely this frequency.

In her book she gives detailed information on the targeted weakening and elimination of pollutants and parasites through fine electrical stimulation at specific frequencies. To free the excretory organs she developed recipes and instructions such as liver cleansing cure, kidney cleansing cure and intestinal cleansing cure.

For Dr. Hulda Clark her discovery seemed to indicate the following: the resonance effect by precisely hitting the natural frequency is not mandatory for the efficient weakening of parasites, bacteria and viruses, whereas the square wave and the positive offset are more relevant. This seemed surprisingly simple and required "only" a simple zapper (suitable for do-it-yourself construction), which needed only one frequency to work.

In her future books, Dr. Hulda R. Clark slightly qualified these statements by introducing the so-called target zapping or plate zapping with a metal plate in-between. On this metal plate - which dealt as a kind of filter - additional "information" could be placed, i.e. swung ampoules or original substances. Plate zapping is nothing else but a simplified bioresonance application.