The Electro-Psychometer, or E-meter is a modified lie-detector. The circuit is basically a Wheatstone Bridge, measuring resistance through the body between two 'soup-cans' held in the hands, most of the variation being due to variations of moisture on the hands (also known as galvanic skin response). For self-auditing there is a modified version that can be held in one hand, while notes are written with the other. As with other devices that measure resistance, there is also a control (called the 'tone-arm' by Scientologists) to set the needle display to zero in normal circumstances and compensate for damp conditions, flattish batteries etc. As with a lie-detector, the session begins with test questions to ensure the device appears to be working properly. As with other Scientology products, they are very highly priced, and members are encouraged to have have at least two (imagine being caught without a spare). As with other lie-detectors, the responses can be faked - remember the case of Aldrich Ames of the CIA (and also the KGB).

Despite admissions that the E-meter cannot detect ethics violations (it would be hard otherwise to explain why the hosts of 'renegades' were never detected) they are still used for 'Sec-checks' in which members are interrogated to discover their 'crimes' against Scientology. They are not supposed to be used in the more serious "Comm-Evs" (Committee of Evidence - a Scientology drum-head court martial).

"EVIDENCE - Spoken words, writing, documents. The E-meter may not be used as it does not register lies on criminal types. Hearsay is inadmissible but statements that one heard another make damaging remarks, saw another act or fail to act are admissible". HCOPL 7 Sept 1963