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Thread: Which scale is trustworthy and most true?

  1. #1
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    Question Which scale is trustworthy and most true?

    I have been weighing myself as part of a weight loss programme at a commercial set of scales in Newcastle's Grainger Market (See attached image) Needless to say, they are calibrated on a regular interval by people from weights and measures.

    Today I purchased a set of digital electronic bathroom scales.

    Both scales weighed me at different values

    So which one should I trust, assuming both are sited correctly?

    I assumed an electronic one would be more accurate as it is not dependent to much on mechanical mechanisms, but the one in the market is regularly checked.

    If the electronic scale is to be considered unreliable, how can manufacturers and retailers get away with selling them?

    Which scale should I trust to give me a true reading as to what my weight is.

    Incidentally the other image is a comparison of me in December 2009 and me last week
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  2. #2
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    Don't trust the one you purchased to be reliable for an absolute reading of weight, though it may well be quite good for tracking changes in weight over time.
    You did remember to wear exactly the same clothes and shoes while taking the comparative measurements, right?

    If you try to weigh yourself on both wearing the same clothes and shoes several times, each time noting what they say, you should be able to make a conversion table so you can use your home scales and by converting know what the other would have shown.

    Apart from that, the best indication that your weight loss program is working is the two pictures of yourself you posted, there's a clear and definite improvement.
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  3. #3
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    Quote Originally Posted by HenrikOlsen View Post
    You did remember to wear exactly the same clothes and shoes while taking the comparative measurements, right?
    I did exactly that today.

    I even followed the protocol I do at the weigh house, by emptying pockets, removal of all footwear including socks and removal of watch.

    I even made sure I did not eat or drink anything or go to the toilet when I weighed myself for the first time on the electronic scales to try and ensure consistency for the comparison.

    If bathroom scales are not to be considered reliable, how do they get away with selling them?

  4. #4
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    I've noticed my non-digital bathroom scale gives different readings depending on whether it is put on a tile floor or on a carpet. Does that happen with digital scales?

  5. #5
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    Have not tried that, but the scales are on the bathroom floor which is tiled.

    My analogue mechanical bathroom scales fluctuated in their reading depending how you stood on them, where as the digital one does not have that issue.

  6. #6
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    Quote Originally Posted by Sticks View Post
    If bathroom scales are not to be considered reliable, how do they get away with selling them?
    By not claiming they are.

    Does it have a button for setting the zero weight? All the digital scales I know needs zeroing in from time to time. Come to think of it, so do the mechanical ones, they just do it with a little wheel thingie.
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  7. #7
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    Bathroom scales, like most measurement devices, tend to be fairly repeatable around the same point, particularly if they have a zero. Anything you use should be good enough to track weight loss if you use them in a consistent fashion.

  8. #8
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    A picture of the scales in question http://twitpic.com/226ba5

  9. #9
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    A person's weight fluctuates by a few pounds even within the day. It would be difficult to compare two devices, by using body measurements, unless they were side by side.

    Still, I'm with the others--body weight scales are not sold for commercial use, so they can be made cheaper--more affordable.

  10. #10
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    Most if not all home-use scales are marked "Not legal for trade," either on the scale or the box it came in or the user's manual. That's pretty much a flat-out admission that they are not that accurate. However, if they give you consistent readings on successive weighings (say, 6 in a half hour or less) then it's good enough to keep track of fluctuations in your weight.

    Fred
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  11. #11
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    How about carrying your home scales into the market and weighing yourself on both in quick succession, eliminating all the other variables? Or even set the home scale on the platform of the commercial one and read both at once? You'll be off by the weight of the home scale, of course, but you can then weigh yourself without it on the commercial one and subtract.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  12. #12
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    I was really annoyed by my bathroom scale. It was off by quite a bit. Then I bought a Wii Fit. It is also off by a bit, I weighed in at the doctors and in the same clothes weighed in on wii and it was 4 lbs off. But on the plus side, it has a chart feature which removes the possibility of forgetting exactly how much you weighted the day before. It makes me happy, even if it is "wrong".

    Solfe

  13. #13
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    Quote Originally Posted by Trebuchet View Post
    How about carrying your home scales into the market and weighing yourself on both in quick succession, eliminating all the other variables? Or even set the home scale on the platform of the commercial one and read both at once? You'll be off by the weight of the home scale, of course, but you can then weigh yourself without it on the commercial one and subtract.
    Or measure an object of known weight, such as one liter of water.

  14. #14
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    Quote Originally Posted by whimsyfree View Post
    Or measure an object of known weight, such as one liter of water.
    That only works if it's already been proven linear up to the total weight it's supposed to weigh.
    That's definitely not a safe assumption without extra measuerments.
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  15. #15
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    Can I suggest something Sticks? Have you tried going into Boots (chemist) they have electronic scales and will give you a reading and a print out too (it used to cost around 20p) then triangulate the amount of weight to an average reading. Plus you can see what readings are closer to one another for future reference.
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  16. #16
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    If the electronic scale is to be considered unreliable, how can manufacturers and retailers get away with selling them?

    Which scale should I trust to give me a true reading as to what my weight is.


    All measuring devices have tolerances for accuracy. For extremely expensive laboratory instruments, the tolerances are orders of magnitude tighter than for commercial scales, which in turn are more accurate than inexpensive home equipment. The question becomes "how much accuracy do you really need?", followed by "how much accuracy can you afford?"

    For an inexpensive home scale, I'd rate consistency at least as high as accuracy. If you're really after accuracy with a home scale, develop a calibration table using sets of known weights through the full range of the scale. Since the commerical scale is calibrated regularly, measure the weights of your calibration objects (such as a set of barbells) to get a reasonably accurate set of values. Next, weigh those same objects on the home scale and record those values as well to see how well they compare.

  17. #17
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    Sticks,
    My sympathies!
    I'm trying nto loose weight too, and I weigh myself every morning, before my shower, after I have been to the loo, naked.
    My weight varies by as much as two kilogrammes!
    It's not the scales, it's physiology!

    It would be better if we BOTH weighed ourselves once a week, same day, same conditions - naked is best - to smooth out short term variations in our actual body weight and lookked for a long term improvement!

    John

  18. #18
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    Quote Originally Posted by HenrikOlsen View Post
    That only works if it's already been proven linear up to the total weight it's supposed to weigh.
    That's definitely not a safe assumption without extra measuerments.
    Linearity is generally assumable at first, though I have encountered scales that had a tendency to underweigh at large weights. One liter was only an example. He could substitute, say, 100 liters.

  19. #19
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    Quote Originally Posted by JohnD View Post
    Sticks,
    My sympathies!
    I'm trying nto loose weight too, and I weigh myself every morning, before my shower, after I have been to the loo, naked.
    You must have a far more permissive pharmacy than the one where I tried to do that.

  20. #20
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    Quote Originally Posted by AGN Fuel View Post
    You must have a far more permissive pharmacy than the one where I tried to do that.
    I typed a reply but the system lost it

  21. #21
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    Quote Originally Posted by AGN Fuel View Post
    You must have a far more permissive pharmacy than the one where I tried to do that.
    At the weighhouse I hear that one guy strips down to his boxer shorts although some says he is a boxer.

    If I find a Boots machine I would have to follow the same protocol as for the weighhouse

    • Wear a light tee-shirt
    • Do not eat breakfast at home
    • Only have a porridge and a coffee at a certain branch of McDonalds
    • Do not eat or drink anything (Even water) before being weighed
    • Go to the toilet before going to get weighed
    • At the weighhouse, remove all items from pockets and remove watch
    • Revove socks and shoes
    • Request weight reading in Killogrammes


    Had I known about the boxer before I started getting weighed I would have been adding, remove shirt and strip to waist, so I could wear whatever shirt I wanted on the day

  22. #22
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    The balance scale remains among one of the most accurate scales today, and is commonly used for calibrating test weights. For weighing heavier masses (people, beef), designs with an off-center beam and a poise (small, sliding weight used for fractional weight measurements) are used. For very heavy weights (trucks) a cantilevered beam system is used.

    Household bathroom scales may be "electronic," but they're often off by a couple of pounds.

    Go with the commercial scales.

  23. #23
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    Quote Originally Posted by mugaliens View Post
    Household bathroom scales may be "electronic," but they're often off by a couple of pounds.

    Go with the commercial scales.
    Which means I ballooned on Saturday

    Today, I was back at the doctors where I was first weighed at 128Kg and on their scales which are callibrated annually I came in at 108Kg a drop of 20Kg measured on the same scales.

    My scales this morning were saying 109Kg and I think that was my weight with nothing on rather than light clothing.

  24. #24
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    Mugs said "often off by a couple of pounds", which means having a reading of 109kg even if you're really 107 kg is well within that variation.

    I will repeat what I said before take a set of matching measurements, preferably by bringing your scales with you when you're getting weighed.

    Record the two measurements, do it a couple of times and see if they fit reasonably linearly in an X-Y scatter graph.
    If it is fairly linear (it can't be entirely linear because the scales are rounding to the nearest number they can show), then you can use the graph to convert from the numbers your scales show to your real weight.

    If you don't make such a conversion to real weight, then having your home scales is going to be a long series of small discouragements because you'll think you gained weight each time you step on them after having weighed yourself on calibrated scales.
    __________________________________________________
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  25. #25
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    I have tried weighing suitcases on bathroom scales of various kinds, and putting one directly on the scales doesn't give a remotely sensible reading. It seems to be because it does not contact the pressure sensors in the right way. It is expecting a person with two feet to stand on it.

    I have also tried weighing suitcases on bathroom scales of various kinds by difference, ie weighing me vs weighing me+suitcase. Again I have not got remotely sensible readings, sometimes the suitcase has a negative weight by this method. I think this is because typically I redistributed the pressure on my feet when holding a the suitcase, and one way of changing the reading big time on a bathroom scale is to lean to one side or the other. Maybe if I could balance the suitcase on my head I might get a sensible reading. I find I am quite good at judging whether a suitcase is within (Ryanair) weight limit just by picking it up, so I don't really need the balance. Since my wife is of the opinion that stuff squeezed in at the last minute somehow weighs less than if they were put in earlier, scientific approaches don't work to well anyway.

    I conclude that typical bathroom scales are very primitive devices. The weight they show seems to depend substantially on the way the weight contacts the pressure sensor. If they work even to 2% accuracy (2kg in 100kg) I would be surprised.

    How can they get away with selling them? By not making excessive claims for their accuracy. The package may have said "reading to one decimal place", but that does not imply its accuracy is to 1dp. In fact I suspect they probably made no claim whatsoever for its accuracy. Legally, all you were buying was a bathroom ornament. Precision instruments cost money, and probably require time-consuming procedures for repeatability.

  26. #26
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    Quote Originally Posted by Ivan Viehoff View Post
    I have also tried weighing suitcases on bathroom scales of various kinds by difference, ie weighing me vs weighing me+suitcase.
    Same here, and have experienced the same issues concerning accuracy. A couple years back I purchased a suitcase weighing device called "balanzza." I have this model. It's the size of a suitcase handle, and displays in both kg and lbs. A simple strap goes through the suitcase's handle, and you pick up the portable scale (about 1 lb), which lifts and weighs the suitcase by averaging readings over about 3 to 5 seconds.

    I checked its accuracy by weighing an empty 5 gallon bucket with my postage scale, then filling it with 5 gallons as measured using a large and accurate 4l lab flask. The results are that the scale is 0.4 lbs off calculated.

    It's great for weighing bicycles, backpacks, and daypacks, too!

  27. #27
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    Quote Originally Posted by mugaliens View Post
    I checked its accuracy by weighing an empty 5 gallon bucket with my postage scale, then filling it with 5 gallons as measured using a large and accurate 4l lab flask. The results are that the scale is 0.4 lbs off calculated.
    That's a little under 1% error. I'd say very good for what is essentially a spring balance.

  28. #28
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    My advice is, forget the scales. Just keep getting fit and eating right, and leave the exact numbers to the mathematicians.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  29. #29
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    Quote Originally Posted by Ivan Viehoff View Post
    I have tried weighing suitcases on bathroom scales of various kinds, and putting one directly on the scales doesn't give a remotely sensible reading. It seems to be because it does not contact the pressure sensors in the right way. It is expecting a person with two feet to stand on it.

    I have also tried weighing suitcases on bathroom scales of various kinds by difference, ie weighing me vs weighing me+suitcase. Again I have not got remotely sensible readings, sometimes the suitcase has a negative weight by this method. I think this is because typically I redistributed the pressure on my feet when holding a the suitcase, and one way of changing the reading big time on a bathroom scale is to lean to one side or the other. Maybe if I could balance the suitcase on my head I might get a sensible reading. I find I am quite good at judging whether a suitcase is within (Ryanair) weight limit just by picking it up, so I don't really need the balance. Since my wife is of the opinion that stuff squeezed in at the last minute somehow weighs less than if they were put in earlier, scientific approaches don't work to well anyway.

    I conclude that typical bathroom scales are very primitive devices. The weight they show seems to depend substantially on the way the weight contacts the pressure sensor. If they work even to 2% accuracy (2kg in 100kg) I would be surprised.

    How can they get away with selling them? By not making excessive claims for their accuracy. The package may have said "reading to one decimal place", but that does not imply its accuracy is to 1dp. In fact I suspect they probably made no claim whatsoever for its accuracy. Legally, all you were buying was a bathroom ornament. Precision instruments cost money, and probably require time-consuming procedures for repeatability.
    The scales you tried must have been designed by geeks who were trying to reinvent the wheel, or perhaps were trying overzealously to cut costs. My old mechanical scale is almost immune to off-balance loading. I leaned from side to side and front to back, on one foot and then the other, almost to the point of falling off, and the reading varied by less than two pounds, and perhaps less than a pound. I can lift a suitcase and lean as needed to stay balanced, and it works fine.

  30. #30
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    I swear my scale is broken. I've been eating much healthier and less, and have been working out consistantly, for a month now and it says I haven't lost any weight!

    . . . okay, I probably haven't because most of my work outs have been with my legs (running, biking, squats, etc) since I don't have my freeweights to lift yet, and I bet I've put on 10 lbs in muscle per leg! (okay obviously not that much). Signups for a semi-local (about an hour drive, ugh) fall soccer league are Saturday; I don't know if I'll have the money or be able to make the drive, but I'm considering driving out for 'orientation' just to see where exactly the field is and if the drive is something that would be possible. That should help with the weight loss.

    Sticks; is there any particular reason you need such an accurate measurement of your actual weight? I'm just curious; relative weight to track weight loss seems adequate. And whatever you're doing seems to be working; you look like you've done great over the last year or so (or whatever you said the time difference was in that before / after pic).

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