This article is from the New Readers Scientology FAQ, by rkeller@netaxs.com (Rod Keller) with numerous contributions by others.
Answer By: Chris Schafmeister <schaf@cgl.ucsf.edu>
An E-meter is a simple device which measures electrical resistance across
the range of 3000 ohms to 7000 ohms at its least sensitive setting to 4500
ohms to 5000 ohms at its most sensitive setting. Scientologists believe
that the E-meter reacts whenever they think about spiritually important
topics. Scientologists use E-meters by holding onto two electrodes while
they sit in a room with another person who repeatedly asks them questions
about traumas from their life or putative past lives until the E-meter
reacts in a way described by L. Ron Hubbard. Scientologists believe that
once the E-meter acts in a predetermined way when they are asked a
question, that the subject of that question no longer influences their
personality. I have played with an E-meter and observed that my body
electrical resistance changes rapidly over the course of tens of seconds
in a random way. The E-meter needle motions did not appear to be
correlated to my thoughts. My training as a scientist has lead me to
conclude that the physiological reason why the body electrical resistance
changes over the course of seconds is due to ion channels in cell walls
opening and closing under semi-automatic control and that Scientologists
train themselves to control their body resistance through a process of
biofeedback. Scientologists then fall deeper into the cult when they see
what appears to be conformation of Hubbard's writings but is actually
their own self-delusion.
 
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