As the UK’s metric changeover drags on with no end in sight, we consider if the advantages of encouraging widespread use of the centimetre outweigh the risks.
UKMA recently received this message through the contact form on its website, www.ukma.org.uk :
More and more I am concerned to see the widespread use of cm as a measure of dimension, by manufacturers and even by the BBC for depth of snow for example, instead of mm, being the SI unit of length which was agreed and adopted.
Unless something is done to address and halt this practice, I can see the mm disappearing from common use altogether, other than by engineers and scientists …”
The Secretary of UKMA replied as follows:
Thanks for your e-mail.
Anne Attlee (daughter-in-law of Clement Attlee, who was PM from 1945 to 1951) ran a campaign from the 1980s onwards entitled “Metric sense”. This was in response to populist pressures, then as now, holding up the UK’s metric changeover. “Metric sense” argued that the British require measures that are familiar in scale to their Imperial equivalents. In most instances, this was easy: yard-metre, pound-kilogram, ton-tonne. For energy, it was accepted that we would continue to use the kWh rather than change to the joule. And for the inch, “Metric sense” suggested the centimetre would make for an easier transition.
I recently encountered some of the resulting problems and wrote an article on about them which was posted on Metric Views in January:
As I mention in the article, I worked in the construction industry from 1965 until my retirement in 2000, covering the period of its metric changeover. A decision was taken early on to use multiples of 1000 whenever possible, and I do not recall a single instance during the transition period when this caused me a problem. Clearly, it was the right decision, and my recent experience of working with my sons in France reinforces this view. But I do not think it was intended that it should apply in general to the wider economy.
As far as I know, SI does not discourage the use of the prefix ‘c’, and it is indeed listed in Table 5 of the SI brochure. Another common example of its use is cL. The Met Office advises that mm should be used for rainfall and cm for snow. Centimetres are normally used for human height, for example at the doctor’s surgery and on fairground rides.
The UK was one of the first countries in the world to adopt SI. The problem we face now, if we are to prosper in a metric world, is to ensure people are more familiar with SI measures than with Imperial. Perhaps popular use of the centimetre, and the resulting risk of confusion, is a small price to pay.
Readers’ views are welcome on this trade off between, on the one hand, the ease of persuading a public familiar with the inch to use a unit similar in magnitude, namely the centimetre, and on the other hand the resulting risk of confusion and costly mistakes.
As there are now around 200 countries around the world that use the metric system as their primary system of measurement, we in the UK are surely not the first to face this dilemma. In particular, many Commonwealth countries that formerly used the inch have now “gone fully metric”. How did they proceed?