Accurate bathroom scales

[Mike Lane]

I hope this is not considered too OT for this group (my apologies if it is).

My question is how much does one have to pay for digital scales with good precision and accuracy?

I use at the moment a Salter digital device costing around £20 (I think). This gives a reading to the nearest 0.2 lbs (or 0.1 kg), but readings can vary by +/- 0.5 lbs, so that it is possible to get two readings for the same object (usually myself ;-), which differ by as much as a pound.

What annoys me though, is that the device seems to use a form of electronic trickery to simulate a greater degree of accuracy than it actually has. What happens is that if you repeatedly weigh the same thing, it will always give the same reading. Whereas if you weigh something different in between two repeated weighings it can then vary by up to as much as a pound. If it wasn't for this I could simply do several readings and take an average.

Medical scales are available e.g.

They will read accurately to +,- 50 g which would be excellent *but* they cost over £200. I suspect though that a fair proportion of the price is due to the cost of certification - necessary of course for medical use, but not for me.

I wonder if some thing in between, for example

do the job as well?

Sorry if this all sounds a bit obsessive but I hate measuring *anything* inaccurately.

[Andy Hall]

Do you want resolution or accuracy or both?

I have a Seca scale which is same internals and electronics as the medical grade one but without the approvals (and inherent costs)

very good product.

[Mike Lane]

On Mon, 3 Mar 2008 14:49:57 +0000, Andy Hall wrote (in article ):

Both really.

Yes it looks good, but still quite pricey at £188, if it's not medically certified. What is the resolution? The blurb says ''Large LCD figures display the patient's weight to the nearest 50g." while the specs say 100g.

[sm_jamieson]

Its probably plus or minus 50g meaning 100g resolution, and some bad english ! Simon.

[Andy Hall]

It's 50g. I just got on it and checked. You can get a version that speaks your weight. I tried one, but it said "One at a time, please",

If you want a medically certified one, then for electronic, you are going to pay north of £200.

For weighing me, I was looking for something consistent with the surgery scales over a reasonable period of time. (it is - I've taken them along a few times).

[Tim Downie]

Sometimes though, it's unhealthy to be too obsessive about body weight measurement. Unless you'e on dialysis, you really don't need that kind of accuracy and it's all too easy to fret about small changes that occur on a day to day basis.

Tim

[Dave Baker]

I understand your POV. I too hate doing anything or measuring anything innacurately and yes it does verge on an obsession which hinders me from just finishing jobs and getting shot of them if there's even the tiniest discrepancy which I know will make no difference and will be undetectable to the customer but if I know about it I have to do it again until it's perfect. My digital scale which I use for balancing engine components indicate to 1g and weigh up to 5kg. Each time you switch it on and it zeroes itself the indicated weight of a given component can vary by 1g although it will then continue to give the same weight in that session for multiple components which do in fact weigh the same. So it causes no problem in balancing things but cannot precisely say what they weigh to the exact gram. Your case sounds a more extreme example of the same thing. A device which has a small resolution but a larger error in repeatability. What you have to pay to get an improved version I can't help with though.

[Mike Lane]

On Mon, 3 Mar 2008 15:58:46 +0000, Andy Hall wrote (in article ):

OK thanks very much. It looks as though this might be the one for me even though the price is somewhat eye-watering compared to something from Argos which looks just the same :-)

I don't think I need one that speaks (unless it did so *very* quietly :-).

[Andy Hall]

Solid and heavy product made in Germany rather than China. I don't think you would be disappointed once you get over the price.

If this is mainly for personal weight monitoring, then long term consistency is more important than absolute accuracy.

[Anita Palley]

This question is off-topic. I for one will NOT be answering it.

Thank you.

[DM]

... but you did answer- just negatively.

Very few things are OT on uk.d-i-y if you look at it

in this case the OP just wants to accurately/repeatably monitor his weight himself.

cheers

[robgraham]

I don't know how much you paid for your scales but to get repeatability at an accuracy of 0.02% is asking quite a lot. I do take it you had thought of that?

[Mike Lane]

On Mon, 3 Mar 2008 19:22:58 +0000, Anita Palley wrote (in article ):

It's absolutely fine not to answer. Why should you if you don't want to?

As a matter of interest though, I wonder why you find this question more off-topic than (for example) Earthquakes, Plastic Bag Usage, The National Grid, Computer Network Routers, etc etc?

[Clive George]

Now there's a thought, the d-i-y National Grid. Taking cues from the current crop of community-led and other information and distributed computing projects (wikipedia, openstreetmap, heck, torrents, SETI, etc), this project attempts to build a coherent national grid entirely on open source principles. It will allow all the microgeneration projects to link up an form an open alternative to the monopoly we have currently. First question, AC or DC?

cheers, clive

[unopened]

Given that this is uk.d-i-y, perhaps you might consider designing and building your own? I don't know how practical it is (but that hasn't stopped many d-i-y projects) but building your own weighing mechanism could be instructive.

Now, the question is, what designs would people favour for self build? Would a 'simple' steelyard be both sufficiently accurate for the OP's purposes, and sufficiently repeatable?

Sid

[Mike Lane]

On Mon, 3 Mar 2008 21:57:45 +0000, [e-mail] wrote (in article ):

Yes it would be ideal if only I had the space in my bathroom to accommodate it. Unfortunately constructing one from scratch is well beyond my capability (and inclination).

[DM]

Measurements at 2x10^-4 resolution and repeatability are fairly routine, certainly length at this sort of resolution isn't a great problem, a decent mechanical vernier will do it. Accuracy of course is a totally differnt matter

IMO it's when you get an order of magnitude further that things get interesting and of moderate cost, and then hitting 10^-6 where it becomes pretty challenging, to say the tleast.

Of course Dave only has a resolution and short term repreatability of

2x10^-4, the absolute accuracy will be considerabley worse, unless regularly calibrated.

cheers

[Tim Lamb]

One point to consider is the type of flooring. Conventional spring scales are (in my opinion) useless if stood on carpet and dubious if on t&g. My bathroom has cork tiles and I can gain or lose 1% simply by shifting the scales.

regards

[geoff]

In message , Andy Hall writes

Yeah - who actually wants scales that tell the truth ?

Personally, all I want is to see a downwards trend

what is the point of scales which weigh to 50g?

before or after a cup of tea ...

[geoff]

In message , Mike Lane writes

... ...

So why weigh yourself at all then ?

What does it actually mean ?

So you drink a mug of tea, that's a 300g increase, take a piss, you lose it