Connected Segmental Body Composition Monitor Scales - how can this work? - Page 1
Forum section: electronics / general

author: peter-h
author_rank: Super Contributor
timestamp: February 15, 2020, 09:37:29 pm
content: https://tanita.eu/rd-545I wonder what it can do beyond measuring the resistance of your feet. But it claims to do much more.

author: ebastler
author_rank: Super Contributor
timestamp: February 15, 2020, 10:38:47 pm
content: It can probably determine your weight.And hey, it'sconnected!

author: Cyberdragon
author_rank: Super Contributor
timestamp: February 16, 2020, 05:00:36 am
content: Quote from: ebastler on February 15, 2020, 10:38:47 pmIs it even a real scale?And no, it couldn't accurately measure your body resistance since skin resistence fluctuates with moisture.I bet Micheal Reeves could make this scammy POS much more interesting...just add two electrodes to a normal scale and call it the same thing...you would quickly learn to never again touch quack medical crap.

author: Raj
author_rank: Frequent Contributor
timestamp: February 16, 2020, 08:55:13 am
content: Ultrasound bone density meter I guess?Edit: attached a screenshot...I ain't no doctor, but it looks like a bull-crap thing to me

author: Rerouter
author_rank: Super Contributor
timestamp: February 16, 2020, 09:17:29 am
content: Those body resistance measurement... I pretty much rule them as quack science used to sell products.I'm not particularly healthy, the machine gave me a perfect score with whatever printout he was using, (shows green and red bands, and I was dead on center each time) I half wonder if it was some default printout after writing this out, as he saw me as the harder sale.My insanely healthy aunt was completely in the red, and he wanted to sell both of us all kinds of crap to "make out scores better", I called him out on in what way exactly was my score meant to improve?As he was swapped out a day later for a different person on the cruise, I asked my aunt that had already sunk $300 on the crap without opening it yet to drink 2L of water an hour before seeing the new guy (free crap on a cruise), suddenly all her scores where on the opposite side of the first test and she was a little pissed at me for spoiling her with reality.I see it mostly as measuring how hydrated you are, and possibly how salty you are.

author: peter-h
author_rank: Super Contributor
timestamp: February 16, 2020, 11:41:13 am
content: I can see it could be doing a couple of things e.g.- a straight resistance measurement (likely to be useless because most of the conductivity is the skin and how dry it is; the stuff inside the skin is very conductive)- a capacitive measurement (could perhaps detect the % of fat - in the feet but obviously not elsewhere)Re the claim about measuring bone mass, I can't see how you could measure it. Resistively, no, because the skin dominates. Capacitively, no, because the conductive tissues surrounding the bones will dominate. And obese people tend to not have correspondingly obese feet... well not until they get really massive, or have heart or other circulatory issues when the feet fill up with water.

author: Rerouter
author_rank: Super Contributor
timestamp: February 16, 2020, 12:02:19 pm
content: What you could possibly determine some information with would be something like voltametery, different tissues have different delays and behaviors, e.g. certain salts do not dissociate until a certain time or voltage is applied, and usually there is a historesis, I know the "fancier" ones of these tend to have a waist high bar to place your hands on, which could improve the effect, but It still leaves me very suss, possibly if you used high enough frequencies you could use skin effect to subtract out values from the skin and different layers of the person.I still leave there use as quack science, as it seems there would be too many variables to reduce for clean results in the few seconds these machines tend to operate under.

author: PlainName
author_rank: Super Contributor
timestamp: February 16, 2020, 12:14:22 pm
content: I have a similar, but less impressively specced, scale. Not connected, just does the water/fat/something else thing that they all seem to nowadays. My understanding of the how (which is very superficial and I haven't looked into it since I use the scales only for weight) is:There are at least two segments for each foot. That allows resistance of the foot/skin to be determined so it knows what's skewing the reading. A 4-wire thing, maybe. from there the resistance between legs can be determined, and since that has to go across your groin it's a fair estimate of total body resistance - the bad fat is around your innards, which are on top of your legs (as opposed to hanging from your jowls or man boobs).Resistance is just for n00bs, apparently, and the better thing is impedance. Shove an AC current up your legs and you can determine how much is fat because of the impedance vs weight and stuff. It's not going to be accurate to 1g but should be enough to say you're fat, OK or anorexic. My experience with mine is that it is overall quite close to expectations, but some days it is massively off. At least, I assume so - dropping from, say, 16.5% to 13% over a day and then back the next day implies something adrift. Of course, maybe I was particularly dehydrated or something, but generally you ignore the outliers and the average is decent.The other thing to bear in mind is that absolute numbers are largely meaningless. What you really want to know is how it's changing, and if you fat content causes a change in a predictable way then what it says is your fat percentage can be ignored, but just watch that it isn't increasing.For reference, I weigh myself every day when I get up, after first having a pee. I also ensure I wear pants and t-shirt (or hold them) so I'm not varying the results depending on weather and stuff. I've done this through a change of 35kg so can see that the fat % does indeed correlate quite well with weight in the expected range, at least on these scales.The other measurements noted for that app, I have no idea. Could be bunkum or not, but I wouldn't immediately diss them on the basis that I can't figure it out straight off. Just take a look around the hacking scene where you have people figuring out what code is running just from power consumption and other, much cleverer, stuff and it's possible that some of these scales designers have thought outside the box a bit. As a trivial instance, maybe the frequency used for AC impedance is varied so it's tuned to particular types of flesh - fat will be different to muscle which is different to bone. OK, that's not clever - it is a trivial thing, but seems not many have considered it thus far.

author: SiliconWizard
author_rank: Super Contributor
timestamp: February 16, 2020, 02:18:42 pm
content: Body impedance measurement, especially just through bare feet, just doesn't work.I had one scale that had this "feature". As you would expect, depending on how wet/dry your feet would be, you'd get very different results, especially regarding the estimation of body fat. Typically, if just out of the shower with wet feet, body fat % would be estimated much lower than with dry feet.I could notice that when losing fat (after losing several kg of overall weight), the estimated body fat % would indeed decrease, so the principle of measurement itself is not completely bullshitty, but as others have said, the real problem lies in the contact with the feet, and it's all very inaccurate.Pretty useless.

author: daqq
author_rank: Super Contributor
timestamp: February 16, 2020, 08:55:35 pm
content: Electrical impedance tomography is actually a medical thing, where you can get useful results, though more along the lines of shapes of things. But I'd be super shocked if they were actually using it.