The E-meter, originally the electropsychometer, is an electronic device for displaying the electrodermal activity (EDA) of a human being. It is used for auditing in Scientology and divergent groups. The efficacy and legitimacy of Scientology's use of the E-meter has been subject to extensive litigation and in accordance with a federal court order, the Church of Scientology publishes disclaimers declaring that the E-meter "by itself does nothing", is incapable of improving health, and is used specifically for spiritual purposes. Such devices have been used as research tools in many human studies, and as one of several components of the Leonarde Keeler's polygraph (lie detector) system, which has been widely criticized as ineffective and pseudoscientific by legal experts and psychologists. History Electrodermal activity (EDA) is the changing electrical charges observed on the surface of the skin. EDA meters were first developed in 1889 in Russia, and psychotherapists began using them as tools for therapy in the 1900s. Volney Mathison built an EDA meter based on a Wheatstone bridge, a vacuum tube amplifier, and a large moving-coil meter that projected an image of the needle on the wall. He patented his device in 1954 as an electropsychometer or E-meter, and it came to be known as the "Mathison Electropsychometer". In Mathison's words, the E-meter "has a needle that swings back and forth across a scale when a patient holds on to two electrical contacts". Mathison recorded in his book, Electropsychometry, that the idea of the E-meter came to him in 1950 while listening to a lecture by L. Ron Hubbard:p. 64 and Hubbard told of that encounter in a 1952 recorded lecture: Mathison began working with Hubbard in 1951 and that year filed application for his first E-meter patent, U.S. Patent 2,684,670. After the partnership broke up in 1954, Mathison continued improving his E-meters with additional patents (, ), marketing them through his own company and publications, retaining many of the concepts and terms from his time with Hubbard. In a separate line of development, EDA monitors were incorporated in polygraph machines by Leonarde Keeler. Rigorous testing of the polygraph has yielded mixed results, and some critics classify polygraph operation as a pseudoscience. Scientology The E-meter was adopted for use in Dianetics and Scientology when Mathison collaborated with Hubbard in 1951. Some sources say the E-meter was "developed by Volney Mathison following Hubbard's designs", or that Hubbard invented it. Hubbard falsely claimed