### Weighty Matters

Sunday, 26 September 2010The metric

system has some points of genuine superiority to those of the English

(aka American

) system, but that superiority tends to be exaggerated. For example, the every-day English measures for volume tend to be implicitly *binary*, allowing easy halving or doubling. (If base 10 were everywhere superior to base 2, then our computers would be designed differently.)

One of the things that I was told as a child was that the metric system were superior because it measured in terms of *mass*, rather than *weight*, with the former being invariant while the latter would change in the face of a gravitational field. Well, actually, the English system has a unit of mass; it's the slug, 1 lb·sec^{2}/ft, which is about 14.6 kg.

Meanwhile, I observe that, in countries where the metric system ostensibly prevails, people typically use its names of units of mass (gram

and kilogram

) for units of *weight*; they even refer to what is measured as a weight. Now, the real metric system *does* have a unit for weight, because weight is a *force*; weight can be measured by the newton (or by the dyne, which is a hundred-thousandth of a newton). But people aren't doing that; they're using kilogram

as if it means about 9.807 N.

Much as it may be claimed that America is the only industrialized nation not on the metric system, really nobody's on it.

I notice that the Beeb most often wants to speak and write of weight, rather than of mass, but in the most ghastly unit of all, the stone (pronounced /stɛun/, with at least one pinkie extended). The stone is 14 pounds (divisible by 2 and, uh, 7). When weights don't divide into integer multiples of 14 pounds, tradition is to represent weight in terms of a combination of stone and pounds, as in Me mum weighs 19 stone and 12.

Of course, if the Beeb were using pounds at all, there'd be the two obvious questions of