I need to monitor my weight quite carefully. To this end I bought a set of bathroom scales that have a reasonably high accuracy. The scales themselves have a four digit LCD readout. (4 digit readouts are a very common electronic component).

If the scales are set to metric, they are able to weigh people up to 200kg with an accuracy of 0.2kg. If they are set to Imperial, they are able to weight people up to 9st 13.5lbs with an accuracy of 0.5lbs and above that weight, with an accuracy of 1lb.

Thus, if you weight more than 10st the scales loose half their readout accuacy because they run out of digits!

my one tells me that I am 13st 1.25lb and tells me the Fat index by pressing the bloke button ans putting 5 11 into the fields.

Steve, you obviously have a more expensive model than mine - it weighs in units of 0.1kg - mine wieghs in units of 0.2kg.

BTW, I bought mine in 2001.

Mine are about that old too, perhaps 2002.

Hark at us, arguing about the year of our weighing scales!

I have digital scales that (purportedly) weigh to the nearest 100 g. If set to read out in Imperial then it indicates to the nearest 1/4 lb.

The scales are quite new (less than 6 months).

However I am not convinced that they are as accurate as the display indicates.

They replaced an old LED instrument that was quoted by the manufacturer as being accurate to 1% of applied weight, and indicated to the nearest 500 g, or 1 lb.

Easy to see in metric that 1% and 500 g means the indicated resolution applies up to a weight of 50 kg.
The Imperial case is harder to reckon of course.

And 1% of 100 lbs is 1 lb.

Yes of course. But they display in st lb, not lb only (like the US).

That's great. Since the error is 1%, everything works out nicely in metric.
But if the error was anything else, it would make no difference.

The easiest way to check out the accuracy of mine is to use the scales at the work gym that are calibrated every week and compare to my reading at home.

It's important to realize that accuracy and the resolution of the digital display are two different things.

A display may have a resolution down to, say, 1 lb or 0.2kg, but that doesn't mean that the reading is ACCURATE to the nearest 8 oz or 200g.

Oops! Meant "1/2 lb or 0.2kg."

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It's important to realize that accuracy and the resolution of the digital display are two different things.

A display may have a resolution down to, say, 1 lb or 0.2kg, but that doesn't mean that the reading is ACCURATE to the nearest 8 oz or 200g.
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But I think we can safely assume that the accuracy of the scales is greater than the precision provided by the reading. Why would a manufacturer calibrate the reading to a higher precision than the scale is able to measure?

Re the above argument about percentages:
% weight is easier to calculate when measured in kg than when measured in st lb, no matter what the % is.

Re the argument about precision and accuracy:

"But I think we can safely assume that the accuracy of the scales is greater than the precision provided by the reading. Why would a manufacturer calibrate the reading to a higher precision than the scale is able to measure?"

In the example I quoted this was in fact the case. If the scales are accurate to 1% of applied weight then the possible error is greater than 0.5 kg at a weight above 50 kg (approx 7st 12 lb or 110 lb), even though the read-out is still to the nearest 0.5 kg (1 lb). If I recall the maximum load was 120 kg.

It seems logical that the resolution need be no greater than the accuracy of the measurement, but there is equipment where this is not the case.

Some cheap digital voltmeters are typical examples. A 3-1/2-digit display on, say, a 20-volt range will read up to 19.99 volts, giving a resolution of 0.01V, yet the accuracy may be 1% or even less.

>>>" Why would a manufacturer calibrate the reading to a higher precision than the scale is able to measure?"

That is a very good point against metric - why use grams and ml that are too fine for the purposes that they are used for. For science, fine. For filling a tin or a carton, inappropriate.

Forum Owner wrote

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>>>" Why would a manufacturer calibrate the reading to a higher precision than the scale is able to measure?"

That is a very good point against metric - why use grams and ml that are too fine for the purposes that they are used for. For science, fine. For filling a tin or a carton, inappropriate.
>>

Stupid statements like this show FOrum Owner's complete ignorance of what is meant precision and accuracy and how they should be applied.

You haven't answered the question. Why use millilitres to measure, say, sauce when the dispenser that fills the bottles is not accurate to one millilitre.

The whole point about UK units is that they realistically reflect the quantities people use.

Whatever happened to the centiliter and the hectogram?
(I have seen cL on occasion on Indian goods, but mL still predominate.)

Industry avoid them, as they don't absorb binary division. Also, hectos and centilitres are even less well know as millilitres.

Bud: "Whatever happened to the centiliter and the hectogram?"

The centiliter is probably most familiar to Brits as the unit used on wine and liquor bottles, e.g. 75cL. Most probably pay it little attention, however, just picking up "a bottle of whiskey" or "a bottle of wine."

It would be interesting to know how many people could even define a hectogram, even among those who are happy with grams and kilograms.

In metric countries, beer or soft drink production is expressed in hectolitres (100 L). Even in the UK hL is often used in this context.

Why ? Because it's a very convenient size for all kinds of liquids that are mass produced.

If crude oil could only be priced in € or $/hectolitre...

"The centiliter is probably most familiar to Brits as the unit used on wine and liquor bottles, e.g. 75cL. Most probably pay it little attention, however, just picking up "a bottle of whiskey" or "a bottle of wine.""

This would be the case whatever measurements were used. For example, many jam jars remain at 454g. Most probably pay this little attention, just picking up "a jar of jam".

I would have to agree with you on that one Ross. For most items in packets or jars that people buy regularly, they don't bother to look at the weight at all. They just pick up the "right size" jar for their needs, without really worrying about whether it's 1 lb., 500g, or anything else.

Yes, and this was what some people pointed out in respect of the 1995 metrication: that it wouldn't really make much difference.

So in that case eliminating the measurement labels altogether wouldn't make much difference either?

Bud, you are being simple-minded again. Eliminating labels wuld be a rouge's charter and would remove a good deal of consumer protection.

An example of where labels are important - EUropean legislation requreis that all packaged foods carry labels showing the contents of the food. I am diabetic, so I always look at the sugar content. Non-diabetics (who are in the majority) usually do not care.

The point I was trying to make was that the units on the labels DO matter... people who buy milk every week wouldn't read the label, but if someone was in a new place or wanted to compare costs for some other reason, they would need a system of measurements they could understand. Of course, the former are in the majority. They don't care which system. But for the few that want to look, we label measurements. And to them, it does matter which system.

"I am diabetic, so I always look at the sugar content. Non-diabetics (who are in the majority) usually do not care"

also relevent to those "doing an atkins" !

My bathroom scales are the swing dial thingo (no electronics for me, I'm afraid). And they are marked to every second pound, but if you squint, they go as far as 1/3lb.