plot the results in a spreadsheet. Sad, but it works.
I have a digital scale with a big display, but I have a suspicion that it shows subsequent readings exactly the same as the first one if the difference is small, to hide the fact that its accuracy is not good. I get round this by putting half my weight on to do a second reading, emulating someone else in the family weighing themselves, then weighing myself properly again for the third reading.
How's that then?
If it gets warmer _both_ arms get longer - don't they?
Andy
Ours (Tanita) appear to use mathematical rounding to the nearest pound (or half-kilo depending on mode). They're accurate and consistent enough for me to weigh parcels, either directly or, if they're too big to see the display, [(me plus parcel)
- me]. The Post Office have never disagreed with the results.
I noticed my scales start to display the same weight as last use, when I absolutely knew there should be a difference. I now step on the scales carrying a weight of 2kg, then step on again weightless. Works every time.
In theory that may not affect the weighing. I don't remember the details now but ordinary scales and balances are subject to many types of errors, and a Mettler type system using the substitution principle with a single-pan balance avoids those errors.
Same with mine (Aldidl). I just rested a foot on the platform to get a low reading, took it off and then got on. Damned nuisance, as it took a while for the reading to go and also a reading wouldn't appear unless I kept still. Couldn't manage incremental weights, so weighing something that had to be carried was a two-stage job. Eventually I went back to the Krupps platform that was old enough 20 years ago when I was given it to need the dial cleaning to make it readable. Far less complication and time.
Grimly Curmudgeon wrote on Nov 23, 2013:
I used to do exactly the same. It seems to be a 'feature' of most consumer grade digital scales. I'm sure it's a deliberate bit of electronic trickery to simulate accuracy. Most people would test new scales by weighing themselves several times in quick succession. If the scales show the same reading each time they're satisfied that the scales are at least consistent
I got fed up with this a few years ago and splashed out on a medical grade Seca scale
Most of the the time, you'll find out that getting an accurate scale depend s more than enything on luck. There is no proven way to understand whether a scale is accurate or not before bringing it to your home and trying it ma ny times. That being said there are some truely renowned brands known for t he accuracy of their products. You can find some of them here:
Often the accuracy depends on what you stand the scales on. Do not stand them directly on a carpet or or foam back cushion floor. I stand my scales on a square of dense block board.
Do you need absolute accuracy from bathroom type scales or just repeatability? A scale may read consistently, say, 2Kg high but it doesn't matter if you are attempting to maintain or lose weight.
Your weight may change by a couple of 2Kg throughout the day depending on your uptake of food and liquids and rate of sweating or going to the toilet.
I'm not sure that is correct. My scales are self--consistent, but for the wrong reason.
If I do a repeat weighing with my scales it gives EXACTLY the same answer. By experiments I found that it memorises past results and if your weight is close to a recent one it merely repeats the previous result.
Robert
I keep seeing this but I don't see why what they are standing on can matter.
The weight of whoever is standing on them is transmitted through the scales, via their 'detection mechanism' to whatever the scales are standing on. If it's soft carpet then the soft carpet is compressed until it's solid and transmitting the whole weight down to the floor in just the same way that standing them on a piece of wood would.
Is it a myth, or am I missing something?
You are missing experience. Some scales (most I have found) only read somewhere near right on a hard surface.
Not missing experience, just missing an explanation.
Thanks.
That makes sense for mechanical scales but not the digital which we have. This has four feet which extend too far below the plate for the plate to be supported by any carpet (or any carpet we have!) when someone stands on it.
It is what is generally said, but what is the physics behind that?
Chris
Because the scales are flimsy and bend under load, or they've used a single sensor instead of 3 or 4 so applying load with the wrong angle gives an incorrect reading.
I think the base plate flexes. On some the carpet hits the base plate and distorts it. As the scales are designed to be used on a hard surface and for minimum production cost, all materials are as thin as possible.
Just tried this before posting. The difference between the readings on a hard surface and a firm carpet was 40%. The reading on the carpet was lower. The reading on the hard surface closely matches that of the large (calibrated) scales used at my local health centre.
This is digital scale where the platform to stand on is a sheet of glass. Platform top to bottom of feet = 25mm (1 inch). It 4 off feet each of 15mm diameter. For accuracy these feet should be the only point of contact with the floor. If the scales are placed on anything that the feet dig into by 3mm or more the scales become supported by the body rather than just the feet.
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