What Scales? Looking for advice on accurate even at low temperatures.

dragondrop

I'm looking for a set of digital display bathroom scales that remain accurate within quite a wide temperature variation. Say 0C - 30C (winter - summer where I live*). I've found info saying 'they're not' but - has anyone got any tips for a brand / model that doesn't cost the earth that work properly from cold temperatures through to hot?

The problem is...

*I often get up before our central heating warms the house up. In the winter, this means a very cold bathroom. BRRR!
The other morning, our digital (but budget) scales read XX.4 kg.
It was cold.
An hour later - after the bathroom had heated up - and - after I'd had a short walk and a glass of water I weighed XX.1kg. 300g difference.
This lead me to research scales. My suspicions were affirmed. It turns out that 'some' scales have inaccurate readings when they are cold because of the sciency bits are made of metal. The sciency bits contract when it's cold. When this happens, the scales are not accurate.

If you've got any tips, I'm all ears! thanks folks

trigden1991

You consumed water and exercised and your weight fluctuated. This is normal, the scales won't really be affected by the temperatures

etebbetts

I've actually noticed this too! I'll weigh myself as soon as I get up, then there have been a couple days where I start working (I work from home) right away and realize I haven't eaten or had any fluids yet. So I'll weigh myself again out of curiosity, and I'll weigh up to a pound lighter. I have a good scale but it's made out of glass and metal. I live in Boston, and our place stays pretty cold at night. I don't have any suggestions for you for a scale that works, but just wanted to say I've experienced this too!

dragondrop

trigden1991 wrote: »

You consumed water and exercised and your weight fluctuated. This is normal, the scales won't really be affected by the temperatures

Hmm... I personally don't think 'A short walk' wouldn't make someone's mass drop 300g in an hour, especially if they'd had some water as well.

tomteboda

You might find this Consumer Reports excerpt interesting and helpful.

The top four scales were accurate within plus or minus 1 pound from 97 to 100 percent of the time. The Taylor dial scale was accurate to that degree just 13 percent of the time. All scales were at least good at repeating the weight they'd measured. As it turns out, the low-rated Taylor stuck to its guns, consistently repeating a weight that was off

As near as I can tell, the decimal place (resolution, e.g. xx.4 kg) is completely gratuitous. Just as kitchen scales measure in 1g accuracy, bathroom scales (designed for much higher weight loads) measure in accuracies of about 1/2 kg. What that means is that your second reading was within the accuracy range of the scale, and the difference was largely irrelevant.

You will find this behavior in I think almost every marketed scale for mass (nonscientific) consumption. Its really not bad at all; even the most accurate physicians scales only have resolution around 0.1 kg, and need to be calibrated fairly regularly to remain accurate.

Accuracy and Precision

Perhaps a physicist could correct me if I'm wrong, but I don't think the thermoelectric effect due to ambient temperature or mechanical misalignment due to contraction of materials would have much of an effect on your bathroom scale's accuracy, certainly not a greater effect than the innate inaccuracy of the scale. Calibration for low temperature would be an issue for a highly precise (and accurate) laboratory scale, but I think the magnitude of effect would be very small in comparison to the bathroom scale's accuracy.

dragondrop

At tometeboda - thanks a lot for taking the time to share that info & write up a really well considered conclusion.

tomteboda

@dragondrop You're welcome! You gave me something to think about on a long, sleepless night