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Metric to Imperial at Tesco

January 1, 2012
Thanks to @apontzen and @gavinsmart for pointing this one out to me.

So the Tesco guide says that the lb conversions are approximate and has a * to point out that they’ve been rounded to the nearest 1/4lb. Unfortunately, this isn’t true.
Tesco_conversions
It is a great example of the compounding effect of rounding errors.
The google search shows the correct conversion for  1 kilogram = 2.20462262 pounds*  (you can do a conversion in Google just as I have in the image if you didn’t know).
[*I’m aware this is rounded of course]
Google_convert_1kg_to_lbs
So what should the table look like and how far out is it? Which ones are actually ‘wrong’?
Corrected_tescos_conversion
The how far off (lbs) column shows the difference between the correctly rounded version and the one stated on the site.
The how far off (grams) column shows the difference between the second column converted to grams and the first column converted to grams.

Am I complaining? Well, not really. Tescos should know better but it is an easy mistake to make. I would probably have gone with the following chart as being ‘good enough’ although I can see the potential for a little confusion of 0.4kg and 0.5kg both being 1lb.

Corrected_tescos_conversion_simple
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One Comment
  1. singinghedgehog permalink

    The more I thought about this the more obvious it became that the Tesco???s chart is a solution devised by someone who didn???t grow up with imperial units. If there is a genuine need for, presumably older, customers to do their shopping in imperial, then why not do it properly in pounds AND OUNCES. Off I went to Excel and a few minutes later had this offering which I personally would be happy using as, I suspect, would most of the people at whom the original table was poorly aimed.kg
    lb and oz0.1
    0lb 3oz0.2
    0lb 6oz0.3
    0lb 9oz0.4
    0lb 12oz0.5
    1lb 1oz0.6
    1lb 5oz0.7
    1lb 8oz0.8
    1lb 11oz0.9
    2lb 0oz1
    2lb 3oz1.5
    3lb 4oz2
    4lb 6oz2.5
    5lb 7oz3
    6lb 9oz3.5
    7lb 10oz4
    8lb 11ozExcel file is at http://www.singinghedgehog.co.uk/misc/tescokgandlb.xls; interesting bits are in hidden columns!

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