The metric system? Get it wrong and you could end up with a wine rack, says Jeff Howell
Most British people seem to be baffled by the metric system. It is supposed to have been taught in schools for at least 20 years, but few people seem to be able to tell you their height in metres or their weight in kilograms. Apart from builders. The British building industry went metric in 1970. In fact, it went more metric than might have been wise - instead of metres and centimetres, the unit adopted was the millimetre. Now, measuring in millimetres is eminently sensible if you want to avoid ambiguity - you can measure anything from the thickness of an electric cable up to the height of a house using the same units; no commas, no decimal points. You don't even have to write "mm" after the figure - since the whole industry is supposed to be using the same system, there is only one thing your dimension can mean. So town houses are around 5000 wide, door openings are 2100 high, sheets of plasterboard are 1200 by 2400, and each course of bricks measures 75. Brilliant. There's just one catch. The great British public still uses the imperial system.

Now, quite why British school children are still only able to tell you their height in feet and inches, and their weight in stones and pounds, is unclear. My guess is that children learn to associate the metric system with maths and science at school, but are unable to relate it to the world around them. This is hardly surprising when estate agents and mortgage valuation surveyors insist on using imperial measurement. No doubt they would counter with the argument that feet and inches are what people understand. But how are people ever going to understand metric if they never have to use it?

For example, there was a predictable outcry in the media last year when food weights in supermarkets were finally made to go metric. A succession of bewildered old dears was dragged in front of the cameras and quizzed on conversion factors from pounds to kilograms. For supermarket shopping the conversion factor is an irrelevance, of course - you either use pounds or you use kilos. You pick up a lump of cheese that looks about the right size and then you look to see how much it costs. Making a story out of the innumeracy of old age pensioners takes attention away from the real issue surrounding mensuration, which is that, under the last government, weights and measures inspections by Trading Standards Officers were pared down to a bare minimum, and cheating by retailers has become, consequently, commonplace. If ever you need petrol for your lawnmower, take an empty five litre can along and see how much the pump reads after you've filled it up to the line - you'll see what I mean.

The other issue, that the British building industry uses millimetres while our continental cousins use centimetres, shouldn't really make a difference, but it does. Most tape measures are calibrated in centimetres, and it is easy to forget to multiply by the factor of 10, so 3m 40cm can get written down as 3040 rather than 3400. Errors like this can leave an embarrassing big gap in your new kitchen work top.

Fitted kitches, by the way, often exhibit distinctive symptoms of mismeasurement. These are called wine racks. A wine rack under the work top usually indicates a cock-up, or at least a degree of idleness, in the chippy's calculations. Two wine racks are a sign of measurement meltdown.