fake "body fat" scales from Jaycar

The Real Andy wrote in news: snipped-for-privacy@4ax.com:

No no! You get to choose any two, not all three!

GB

I'm not so sure that you've been dudded you know. You paid fifty dollars, and got fifty dollars worth of equipment. Chances are, the guys who designed it were given a price tag to work to. Knowing that one cannot do a *repeatably reliable* measurment for that amount of money, they wrote in a damper that won't allow it to feed you readings that vary from day to day by too much more than an average punter will *actually* vary from day to day.

You'd likely be equally upset if you'd gotten a machine that *did* do a raw calculation every day, but did so with a tolerance of

+/- 30%. At least this way you're getting some degree of consistency in the readings, even if it takes several days to average out at an 'accurate' figure.

I think it is fair to suggest that money buys tolerance. The more money you spend on an instrument, the more accurate it is likely to be. It is arguable that by virtue of the 'damper' arrangement, you got a better instrument than you paid for.

Food for thought, if nothing else.

GB

Mike wrote in news:43ec30eb$1 @quokka.wn.com.au:

Now that's just out and out cynical. You bought junk from a business that is widely known for buying up cheap junk and selling it at entertainment prices for entertainment porpoises. To go all "I know my rights" up on their corporate arse is just being silly. You bought a toy: You paid a toy price. You got a toy. Why is it that you're so surprised that you didn't get a precision instrument?

GB

As a comparison, what are the reading you got? Mine was 83.2kgs, 187cm and

27% fat.

Michael

I guess I'm learning. So jaycar are like "Red Dot" or Oakley Electronics?

I'm not at all surprised at the poor precision. Its about +/- 400g for weight. If it came anywhere near that for fat%, I'd be happy. The claim is 0.5% precision. Readout is to the 1/10%.

Jaycar are like "The Reject Shop" or "Everything's $2". A substantial (and growing) portion of their business involves buying up whatever is (1) vaguely electronics related and (2) cheap from distress sales, dodgy importers, etc and on selling it to their retail customers. That portion of the business has a constantly rotating stock that, once sold, you'll probably not see again. They've probably got a container load of these scales to shift, and when they're gone, they're gone. (Of course, I think the exception to the rule is in the 'Aura Interactor' audio/physical feedback things. I think they got a whole boat- load of those, they've been pushing them for years!)

500g is standard tolerance for entry level electronic scales of this type, so that's about right. I think it's gotta be substantially more difficult to get a repeatable reading on the skin resistance thing though - there's so much that will affect that day to day. G

I love those Aura Interactor things! We extract the shaker mechanism and use it in all sorts of custom built vibration test equipment for geophysical gear. Very useful!

Dave :)

So it won't work with an open circuit.

Has anyone with one tried:

1a. soaking your feet in a saltwater solution before jumping onto the scales (resistance) 1b. using the scales before and after jogging (resistance)

1. putting a thin bit of rubber between your feet and the scales (capacitance)
2. tried to simulate the above with resistors and capacitors of various values

Peter

8<

Terminology correction: Ship-load :)

On Thu, 09 Feb 2006 09:57:25 +0800, Mike put finger to keyboard and composed:

Why don't you just use resistors to test the scales? For example, what about two metal pads connected to a resistance wheel? Stand on the pads in rubber soled shoes.

- Franc Zabkar

--
Please remove one 'i' from my address when replying by email.

I just used people of differing build, and added weights, conducting and insulated. It was inpossible to get a %fat reading off their =f(m) formulae, with constant age/height/sex settings.

The real meters measure more than just DC resistance. See this page:

Jaycar refunded the money. They have changed the packaging in the shops, which now makes no claim of measuring fat. The machine itself still pretends to do it, of course. And even the staff still assumed that it really worked.

I checked out the newer $90 model, which was really bad in so many ways. So its back to the old mechanical model for me.

The funny thing is if they didn't measure body fat at all you would have been perfectly happy with them.

Michael