The stone – now comes with a health warning

The Local Authority Coordinators of Regulatory Services (LACORS) have recently announced that they are launching a nationwide project to deal with inaccurate hospital weighing scales. The project follows studies which found hospital staff using inaccurate and unsuitable scales to calculate dosages of medication for patients.

This link provides details of the LACORS project: http://www.lacors.gov.uk/lacors/Home.aspx

A reader of Metric Views writes:
“This seems a classic area of where the measurement muddle exacerbates the problem.  We are presumably talking here about significant errors in weighing rather than slightly inaccurate scales.  If people knew their weights in kg, then surely they would immediately notice if the reading seemed unusual, say more than 5 kg different from their normal weight.  But if they only know their weight in stones then they would be none the wiser – to their own potential detriment.”

Another reader points out, however, that the Government is already tackling this issue. She writes:
“I noticed again tonight in my local NHS surgery that there is an advertisement in the waiting room for patients to log their own height, weight and blood pressure. I saw several people doing this, using the metric scales, cm measure and BP machine in place. There were no quizzical or confused looks as people wrote in their details (even the elderly).”

But our hapless stone faces other handicaps:

Its plural is a source of confusion. Does she weigh 10 stone or 10 stones?
Its larger relatives, the quarter and the hundredweight, have already fallen into disuse;
Its relationship to its smaller partner, the pound, is thoroughly confusing for those schooled in decimal arithmetic;
It is used only for one purpose, to indicate the weight of people, and stands in isolation from the weight of almost anything else, making comparison difficult;
It has doubtful legal status;
It is unknown in every other country in the world, including the USA, the main bastion of ‘customary’ measures and a major influence on popular culture in the UK.

So to those who prefer familiarity to logic and simplicity, and persist in recording their weight in stones and pounds, Metric Views offers this advice:

Make a note of your weight in kg – tomorrow your life may depend on it

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6 Responses to The stone – now comes with a health warning

  1. Ezra Steinberg says:

    Seems like a great opportunity for pro-metric groups to encourage the appropriate professional groups and stakeholders in the medical profession to switch completely to metric. The media could also be encouraged (at least the official media, like the BBC) to promote the use of only kilograms on both in their news and entertainment programs.

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  2. Martin Vlietstra says:

    LACORS have highlighted a serious problem which is only made worse by the mish-mash of units that are used in the United Kingdom.

    As far as I can see, there are three principal reasons that a person’s weight might be recorded in hospital:

    • To determine a drug dosage where the required dosage is dependent on the patients mass.
    • To determine whether or not the patient is overweight or underweight
    • To monitor weight loss or gain over a period of time.

    In the first two, highly accurate weighing devices are not necessary – a 1% is almost certainly acceptable while I believe that a 5% error would be just tolerable. However, if a patient’s weight loss or gain is being measured and it cannot be guaranteed that the patient will use the same set of scales every time, then a much higher degree of accuracy is called for. (I once checked the cookery class scales at my children’s school and found a 20% error).

    If the purpose of taking a patient’s weight is to monitor weight gain or loss, then rounding errors due to “numeric noise� will cause inaccuracies. For example, if a patient’s weight is measured to the nearest kilogram, then:

    • An increase in weight from 80.49 kg to 80.51 kg will register as an increase of 1 kg (The true increase being 0.02 kg).
    • An increase from 79.51 kg to 81.49 kg will also register an increase of 1 kg (The true increase being 1.98 kg).

    In both cases the first reading will be displayed as 80 kg and the second as 81 kg. If the patient used different sets of scales for the first and second readings, there is scope for errors due to slight differences between the scales being exaggerated. If these weights are now converted to stones and pounds, there is further scope for further inaccuracies due to rounding errors.

    In short, LACORS can ensure that scales are accurate to a certain degree, but if the readings taken from those scales are converted into alternative units of measure, then inaccuracies will result.

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  3. Martin's point about the apparent and true increases in weight makes me wonder about the accuracy of scales used by slimming clubs (like Weight Watchers).
    Are slimming club scales checked regularly?
    Perhaps an apparent loss of 1 kg is really only a loss of a few grams.

    Philip Bladon
    www.simetricmatters.com

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  4. Alex Bailey says:

    Philip's question brings up an interesting point... given that the entire slimming industry insists on using inches, pounds and stones in it's advertising and products, do they even use metric scales or measuring tapes?

    Do laws requiring the use of metric in trade, health, public safety and administration cover slimming clubs? I'm guessing that nobody has ever sued one of these organisations for not losing the weight claimed in the commercials but if they did would it even stand up in court since imperial weights have no legal standing?!

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  5. Martin Vlietstra says:

    The UK Weighing Federation (www.ukwf.org.uk) has put out a very good summary (http://www.ukwf.org.uk/pma/a5colour.pdf) of the law regarding weighing within the medical field.

    In answer to Phil's original question, weighing devices used in health clubs, fitness centres etc do not need to compy with the Non-automatic Weighing Instruments Regulations 2000.

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  6. Richard Blundell says:

    To add another angle to medical weights, I'm a veterinary surgeon and we use kilograms exclusively when weighing animals. For us is essential as all drug dosages are given as milligrams or millilitres per kilogram body weight. The animal's weight in kg is recorded in the records, and I have always told the owners that figure and never once been asked to convert it back into stones or pounds or anything else for that matter. There's no problem here, so I've always assumed the medics do the same.

    PS There was a news story on the BBC about obesity in dogs with imperial measures used, I wrote them an email explaining that we never do that and at least they added kilograms to the stones value, although they didn't replace them entirely.

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