Pardon my scientific ignorance, but what exactly is “electrical impedance on your skin”? And what, if anything, does it signify? Is it a quantity that might change with your pulse or your blood pressure or your temperature? (I believe the “mood rings” popular in the '70s were simply crude thermometers that changed color with body temperature – which might, I suppose, have some relationship to one’s mood.) Hard to believe even the most gullible people would attach any importance to the e-meter, if it gave the same result for every reading; there must be some kind of variation.
And what about the Scientology cross? Why a cross?
Galvanic skin response is a somewhat accurate measure of stress. It’s one of the things measured by a polygraph. There are various ways and places to attach the electrodes to a subject’s skin.
However, the E-meter does not use medical electrodes attached to the skin. It uses cans held in the hands. This produces readings that change due to how tightly the cans are gripped, how fatigued the hands are, and a bunch of other things.
The E-meter uses a needle gauge rather than a digital readout. It does not record data in any manner.
It’s a poor excuse for a piece of medical or scientific equipment.
Based on my knowledge of electricity, which is greater than my knowledge of anatomy & medicine, I think it would be more accurate to call it electrical resistance, not impedance.
Resistance is what impedes the flow of electricity or electrostatic charges. A higher resistance reduces the flow. A galvanometer sends a small current thru the test object and measures how much gets thru.
If you hold one probe in your left hand and one in your right, and the galvanometer measures the flow, the reading is affected by moisture, how good the contact is between the probes and your hand (squeeze tightly, more surface area, better contact, less resistance) and the body’s natural resistance due to skin and organs. Sweat more, less resistance. Room temperature and humidity are also factors; body temperature may be.
I doubt if your pulse or blood pressure would have much effect on the reading. And I know of nothing in medical science that uses such a reading for legitimate diagnosis (but I could be wrong, see previous disclaimer).
Why do some people think the position of the meter’s needle means something other than current flow? For the same reason some people think tea leaves in the bottom of a cup have fortunetelling value, or tarot cards can reveal your personality. Quacks will always be with us as long as there are fools eager to part with their money.
You’re correct… impedance (Z) is a complex quantity, where Z = R + jX. Resistance is equal to the real part of the impedance, thus resistance = Re{Z} = R. If they’re using a DC excitation source then they’re measuring the resistance.
And everything else you said was right on the money, in that just about everything will affect the resistance reading (perspiration, pressure, humidity, contaminates, etc.)