Has SI delivered?

The fuss about measurement units at the start of this century has overshadowed progress thirty years earlier in education, science and engineering. We look at the benefits that were predicted at the start of the transition to SI and ask if they have been delivered.

1960 saw the first publication of standards for the International System of Units (SI), the modern version of the metric system that is intended to be universal in its application. Nine years later, when the UK Metrication Board held its first meeting, it was being said that our country would be one of the first in the world to make the transition to SI and that everyone in the UK would be using it by 1975. That, as we know, turned out to be optimistic. Attention soon switched from the early successes of the metric changeover to the failure to complete it. The work carried out by teachers, scientists and engineers between 1965 and 1975 was largely forgotten. In this article, we consider their achievements.

Sometimes we are led to believe that there was only one system of measurement widely used in the UK before 1965. In fact there were two. Commerce, engineering, manufacturing and primary education normally used Imperial measures, as did the local pharmacy. But science, including research and teaching in secondary schools and in universities, used the centimetre-gram-second (cgs) system. Those working with electricity were often unsure which system they were using! As part of the metric changeover, all would be expected to adopt SI.

In my youth, I learned Imperial at primary school and still remember those never-ending conversions, was introduced to cgs in the first year at secondary school and used this until leaving for university. There, I was taught in a mixture of Imperial and metre-kilogram-second-ampere units (the forerunner of SI), finally moving on to Imperial units exclusively on the construction site. An aim of the adoption of SI in both science and engineering was to smooth such career paths, and Metric Views would be interested to learn how well this has worked for those who began school after 1974.

From the beginning of the metric changeover, The Royal Society and the Council of Engineering Institutions co-operated to promote the adoption of SI – organising conferences, preparing and publishing guidance, and so on. They believed that the scientific community and the engineering profession would carry a substantial share of the initial effort in converting to the new system of measures, and this turned out to be so.

In the construction industry, Imperial units were scarcely fit for purpose – try, for example, to calculate in your head the volume in cubic yards of a trench when its dimensions are given in feet and inches. Perhaps this is one of the reasons the changeover went smoothly – there were immediate and obvious benefits. It was largely complete by 1975.

In manufacturing, however, there were some difficult obstacles to overcome. Joseph Whitworth in the nineteenth century had simplified Imperial by introducing decimal divisions of inches down to the “thou”. Companies often had close ties with US businesses. Directors of many companies, who foresaw difficulty and expense with little prospect of early reward, sat back and hoped for the best. The transition to SI began slowly and programme targets were frequently missed. Many businesses folded before or during the changeover in the face of foreign competition and declining export markets, or were taken over by foreign competitors. Metric Views would like to hear from anyone whose career in manufacturing or mechanical engineering spanned the metric transition. How well was the changeover managed? Did the company that you worked for survive it?

The transition in pure science from cgs to SI may have been simpler, but may also have been ‘more kicks than ha’pence’. Although it involved less fundamental change than that for engineering, the rewards were fewer. The views of scientists who participated in the adoption of SI would be welcome – do you consider the effort was worthwhile?

In the late 1950s, the author and scientist C P Snow drew attention in his novel “The two cultures” to the gulf between scientists and “literary intellectuals”. But there were two cultures within science too – pure science and applied science. The eminent scientist, Dr M J Lighthill FRS wrote in 1968:

“Britain needs large numbers of scientifically oriented people of good ability to be active in the industrial life of the country, but the prestige attached to ‘pure’ scientific research draws them harmfully away from technology and engineering.”

He went on to outline the difficulties faced after leaving university by those who had scientific qualifications and wished to become industrial scientists and engineers. He argued that “the adoption of a common system of units in science and engineering may substantially facilitate the conversion of scientists at various stages in their career to engineers”, and he suggested it would reduce feelings of separateness between pure science, applied science and engineering, leading to “the creation of greatly increased traffic of ideas and people between them.”

Was Dr Lighthill right in his analysis? Has the adoption of SI led to the outcomes he forecast? Metric Views would be interest to hear from scientists and engineers who have bridged or crossed the divide.

Clearly, the metric transition in education was successful. Perhaps too successful, otherwise why should there be talk now of reversing certain aspects? But we occasionally hear that some teachers’ hearts were not in it – they would revert to Imperial as soon as the curriculum was put to one side or, like their pupils, when they left the classroom. And while the transition prepared many students for careers in science and engineering, it left a few retailers and their customers unable or unwilling to cope with the change to metric measures when it finally came. Views of teachers on the value of their contribution to the adoption of SI in the UK economy would be welcome.

It was also suggested in the 1970s that greater familiarity with the metric system among the general public, in their homes, at work and on the high street, would produce a population more at ease in dealing with numbers and better able to earn its living in an increasingly numerate and competitive world. With the metric changeover now stalled in important areas from road traffic signs to screen sizes for TVs and monitors, it is perhaps too early to reach a conclusion on this issue. However, A-level exam results published on 29 January provide cause for optimism. They show that maths was the most popular subject, with 10.6% of all entries, the highest level since records began in 1996.

Concluding where this article began, with science and engineering, we observe that there was initially considerable optimism about the adoption of SI in science and engineering. Sufficient time has surely passed to form a judgement on whether it has delivered on those promises, hopes and aspirations. Let us know your views.

3 thoughts on “Has SI delivered?”

  1. As a mechanical engineering apprentice in the late 1960’s I recall the then recently established Engineering Industry Training Board (EITB) introduced a series of ‘Phase tests’ and ‘Modules’, the purpose of which was to encourage normalisation of apprentice training between providers. From what I remember these were all undertaken using metric units. At the time I found this somewhat challenging since most, if not all, drawings with which I was familiar on a day to day basis were dimensioned in imperial. Machine tools and instruments available to me were also graduated in similar units, resulting in my having to make numerous conversions back and forth between units (with the associated opportunity for error!). This all subsequent to having been taught physics at school in metric units since 1964. Clearly UK industry at that time was ‘behind the curve’.

    The EITB was disbanded by the government in January 1991, six weeks before the then Prime Minister was ousted.

    It should also be noted that the Institution of Engineering and Technology (IET) (the successor to the Institution of Electrical Engineers (IEE), et al) and an affiliate of the Engineering Council currently produces through its subsidiary body, IET Services Ltd., a monthly magazine titled ‘E&T’ that contains a hotchpotch of imperial, US customary and metric units, sometimes appearing in the same article! So much for the Council of the IEE recommending, in April, 1952, that the M.K.S system ‘should be employed by authors in papers submitted to the Institution and that all students of electrical engineering should become conversant in its use’.


  2. It’s hard to see how SI can deliver in the UK when one of the primary areas that nearly everyone acknowledges should use SI, namely science, is being de-emphasized in UK schools:


    This is an ominous trend and bodes poorly for the UK, unfortunately, including fully adopting SI in all walks of life and ending the metric muddle.


  3. Not only is science being squeezed out of British schools, but in a recent interview, the Prime Minister advocated greater use of imperial units in British schools. He overlooked the fact that the switch from imperial to metric units removed large chunks of material from the arithmetic (now renamed maths) syllabus – in the case of primary schools this allowed teachers to spend 10% of the total teaching time on other subjects.


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