A radiesthesist works with a small weighted pendulum, sometimes a rod similar to a dowsing rod, held loosely so it can swing or rotate freely, over a map, a photograph, a sample of food or water, or directly over a person's body. The direction, pattern, or intensity of the pendulum's movement is read as a signal, a clockwise swing might indicate a positive finding and a straight back-and-forth swing a negative one, in whatever specific coding system the practitioner has learned, and is interpreted to answer questions ranging from where underground water lies to which foods suit a particular person or which organ is under stress. Unlike traditional dowsing, which mainly locates physical targets such as water or minerals, radiesthesia typically extends the same basic method into diagnosis, quality assessment, and answering yes-or-no questions more generally, treating the pendulum as a general purpose detector of subtle information rather than only a locating tool.
The practice descends directly from dowsing and shares its central, untested premise: that the human body, or the instrument in the practitioner's hand, can detect a real physical field or radiation too subtle for ordinary instruments to register, and translate that detection into an involuntary, readable muscular movement. Practitioners generally attribute the pendulum's movement to this claimed sensitivity; the alternative and far better supported explanation, consistent with everything known about how the practice actually works under controlled conditions, is the ideomotor effect, in which a person's own unconscious muscular tension, shaped by their expectation of the answer, produces the pendulum's apparently independent movement without any external field involved at all.