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Blog: What's in a number?
How our lives are dominated by numbers yet we somehow get it wrong

4. Beware enormous magnetic fields!

Trucks with magnetic fields exceeding 7.5 teslas are presumably not permitted on this road.

I am still in Plymouth, and quite often I have been walking past some road signs which show a vehicle within a red circle and the characters 7.5T. When I first saw it I suddenly became very frightened as 7.5 T is a very large magnetic field, so the apparent limit on magnetic fields might occasionally be approached. The reason for my fear did not arise from the fields themselves, but rather the fact that there would be possibly dangerous lorries around, carrying superconducting electrical coils, liquid helium in cryostats and so on. The potential for danger from such mobile equipment is obviously quite high. Then of course, I relax as I realise that the sign is simply a weight limit and somebody has got the wrong abbreviation for tonne, which should be t not T. I am of course joking about the physical danger, but in my idle moments I wonder whether I could drive say a 10 tonne lorry down the road in question with impunity. After all, the legal profession is supposed to be logical and the sign does not strictly ban a 7.5 t lorry, but a 7.5 T one which is very different as indicated above.

The abuse of the metric system is not unique to the British road signs, of course. The above example is trivial and of course I was not entirely serious about being afraid! Unfortunately, the abuse occurs elsewhere. The worst excesses that I've seen of an organisation claiming to use the metric system has been JPL in Pasadena, California, the voyager weekly report. Many people worldwide are interested in the progress of the Voyager probes, and the JPL website describing this could be considered a reflection of the organisation itself. At the least it is its "shop window". However, we learn that fuel is being consumed in Gm, time is measured in sec and of course the howlers Km for measuring distance and Kg for measuring mass. Strictly speaking the units as written are:
Gm-- Giga metres; Km-- kelvin metres; Kg-- kelvin grammes

None of these make any sense in the context. Sec is not an agreed abbreviation for anything that I'm aware of. For those of you who are a bit rusty on the metric system, you need to replace the website mistakes by the following:
Gm --> g; Kg --> kg; Km --> km; sec --> s.
There, doesn't that look better already!

While this might seem harmless enough, to me it indicates a lack of respect for an internationally agreed set of units and or some sloppy thinking by the JPL staff. In addition if you are somebody used to seeing the units with proper abbreviations it takes a few seconds to read the numbers and then work out what the author is really trying to say. Come on, JPL, I know you do rocket science, but it doesn't take much effort to abide by the agreements that the US Government has signed up to (if reluctantly).

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Website revised by John Austin, 29/1/2015. © Enigma Scientific Publishing, 2015.