Wild goose hunt

The common polygraph does this among other things, all surrogate markers for a particular state of mind in that case.

The appllication certainly exists.

It diagnoses a state of advanced gullibility in peple who buy this sort of machinery - for example polygraph lie detection equipment - in the expectation that it will do anything useful, and in people who pay good money to be investigated by this sort of machinery.

You pass a low level AC current (at frequencies from 50Hz up to a few kHz) through skin and flesh, and measure the voltage drop along the path (most of which is in the skin).

It isn't difficukt to get accurate and reproducible results, but the results don't tell you anything that is particulalry useful.

--
Bill Sloman, Nijmegen

I think there is an electrical measurement of fractional body fat, but I don't recall how or how well it works.

John

A lot of weight scales have that feature these days, along with some stand-alone gadgets. The weight scales use some kind of "high frequency" (I'm guessing high audio range) impedance measurement through the soles of the feet. One of the Japanese companies has one that uses hands, IIRC.

Okay here's some more info and some good search terms:

"Precisely what BIA measures in terms of electrical and biological parameters is not known and probably varies somewhat from person to person. Instruments for BIA introduce into the body a known amount of current (I ), of about 800 µA, most often at a frequency of 50 kHz. The current passes between two electrodes, often called the source and sink (or detector), and generates voltages between different points in the body.."

DC or very low frequency impedance would probably be dominated by human skin resistance, which in turn would be highly dependent on sweating etc.

Best regards, Spehro Pefhany

--
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Dreadful. First, they (the gadgets or practitioners) ask you for enough height/age/weight/sex info that they should already know. You key all this in, and it spits out something silly.

After a 10k race some years back, a "professional" machine in the festival tents measured me at 16 or 17%, despite my being about 5% then.

The girlfriend's scale--from a well-known and reputed maker--bears a notice that the instrument is highly sensitive and accurate. Sensitive to hydration, that is, and they enjoin the user to use at the same time each day, under the same conditions of hydration. Under those conditions, it rates my body fat the same as hers, but 5-site skinfold puts me at about half.

Completely useless.

James Arthur

Test it yourself with an ohmmeter, likely results:

(1) Hand to hand, dry hands: 10K to 10 megs, depending on your skin thickness, calluses.

(2) Hand to Hand, wetted with water: 1K to 5K

(3) Hand to Hand, sweaty: 500 ohms to 2K ohms.

"Roger Bourne" ...

Goose found...

I've designed big parts of a system like that, some 20 years ago, a "Specific Frequency Impedance Plethysmograph" or "SFIP" for short.

Used a floating four electrode measurement (Kelvin circuit), with some 15 points in the range 10..500 kHz. From the measured impedance and phase one can calculate back this equivalent circuit:

__________ R1 __________ | | |___ R2___ C ____|

R1 is the electrolye around cells, R2 the electrolyte inside cells and C the capacitance of the membrane of the cell. When a person has kidney dialysis water is removed from the body, first from between the cells, then from within the cells. The instrument measures the extraction speeds and can be used to guard or control the depth of the dialysis.

I tested it myself. Big ISA-card in my luggable PC, electrodes on the leg. Drank a lot of water. Pissed it out again. Beautiful measurement data. Then tried beer. Got very drunk. Still worked wonderful - but different data. Can you guess why?

A slight variation of the instrument was used to measure and guard for excess thoraxial liquid (read 'water in the lungs') in unconscious patients.

See also:

Regards, Arie de Muynck

Could you please describe those five sites in more detail?

John

His or hers?

Hmmm, in retrospect, we only used 3 sites, per the simplified Jackson / Pollack. They are: 1) pectoral 2) abdominal and 3) thigh.

Forumlae are given, for example, here as Equation 2:

Pictures of most of the folds are here under "Body Composition":

As far as description, the sites in question are described as "pale-to-light brown, soft, and juicy."

Regards, James

Right- and if Dick Cheney is a member of the hunting party, hit the deck when he raises that rifle...

Its called a 'wild goose chase'. A hunt is usually the precursor to the chase. The chase can only commence once the hunt has successfully located a suitable wild goose specimen.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
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Trust the computer industry to shorten the term "Year 2000" to Y2K.
It was this kind of thinking that got us in trouble in the first place.
        -- Adrian Tyvand

1) If i am wild, and get goosed, shall i honk? 2) Ever heard of Scientology and the E-meter?

The Scientologists routinely use this kind of equipment. The swear it works well, diagnose you with whatever is fashionable at the moment and charge big bucks to heal you.

- YD.

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