No matter what kind of science you want to apply to the E_Meter, you always come back with a "slight of hand" trick (like a magician sawing someone in a box in half). This simple ohm meter, as has been discussed elsewhere in this thread merely measures "resistance" to an electical flow. And I think our resident Electrical Engineer would back me up on this ... an electrical current passed through the body with origination points on each hand would seek the "path of least resistance." That is, it wouldn't go anywhere near the brain -- preferring the center mass of the body (heart, lungs, chest cavity). But then, for SOME PEOPLE, the path of least resistance COULD BE their brain ... ROFL.
And, of course, you must factor in body fat, amount of fluids consumed prior to the test, dry versus oily skin, amount of surface contact on the electrodes, individual sensitivity to electrical current, etc.
If Scientology were REALLY serious about getting bio-feedback from a person's body, then they would use the latest technology for actual lie detectors, or polygraph machines (but then, that system can be fooled also). It would include, blood pressure monitoring, heart rate and breathing ... in addition to measuring perspiration on the skin. These four signals are monitored on a computer by the examiner, in addition to "body language" and "eye movement," and a subjective conclusion is reached as to the truthfulness of the answers. When I had mine done for my gig at the Sheriff's department, I don't remember them suggesting any body Thetan activity (but then, maybe that's in my secret employee file).
The only reason the Scilons use this device, is that the Magic 8 Ball was already invented and patented BEFORE the E-Meter:
I have a rather humorous version of the latest E-Meter technology on my web site, so follow the link below and you'll see what I'm talking about.
Here's the link to the larger version: