on 5/11/03 3:06 PM, John S. Ward at [EMAIL PROTECTED] wrote: Dear John,
I have interspersed some remarks. > Hi Pat, > > I still have a hard time accepting the general message that mm are always > preferable to cm. That's understandable and you are not alone. Many others � even on this list � have trouble with this, and so did I for many years. I simply could not understand why metrication programs using millimetres worked so well, and metrication programs using centimetres hardly worked at all. I kept saying things like, 'Can't they see that it's simple � can't they just move the decimal point'. However, the evidence before me was irrefutable and it would not go away. My conclusions are based on many years of personal observation in many different activities. For example, I directly observed, as a trainer of trade teachers, the ease of the metric transition for these trades: boilermakers, bricklayers, carpenters, fitters and machinists, furniture builders, piano makers, plumbers, and welders. I also observed the difficulties faced by cooks, tanners, and textile workers such as scourers, carders, gillers, combers, spinners, weavers, and knitters when they tried the same metrication process using centimetres. Simply put, if a group decided to 'Go metric' using millimetres, the process was quick and relatively easy. It didn't matter whether the people concerned were scientists, technicians, or bricklayer's laborers. Generally, the metrication process took about a year for most people, with only a few laggards delaying their metric transition for up to three years. On the other hand, if a group decided to 'Go metric' using centimetres, the process is slow, difficult, accompanied by moaning, groaning, and threats of mutiny. Using centimetres, the metrication process for these groups has taken 33 years � so far � and there is no clear end in sight. [As a side issue, this is the path to metrication apparently chosen by the world's computer industry � I wish them well.] > My biggest complaint is that for longer lengths it makes > numbers inconveniently long and difficult to read. > > If you look through your list, most of the professions that use mm are either > technical, or involve small sizes or tolerances more fitting for mm. I > suggest that your mm professions caught on more quickly because they are more > technically minded and measure length more often than, say, a baker, cook, > gardener, or tree surgeon. Think about the bricklayer's laborers that I mentioned earlier. We are not talking about intellectual giants here, but these folk had little trouble adjusting to house plans that contained numbers like 22�800�mm for the length of a wall. One of the reasons for this, I think, is that the big numbers have given their users three distinct advantages on a building site: 1 There are never any fractions. 2 There are never any decimal points. 3 Calculations are mostly simple, but if they're not, they can be fed into a calculator without conversions. If you compare this with the issues confronted by a textile worker (say a weaver) who still has to: 1 Negotiate halves and maybe quarters and eighths of metres and centimetres. 2 There are almost always decimal points with varying numbers of digits to the right of them. 3 Calculations might involve fractions, decimals or both of these. For example, how many 7 1/2 centimetre squares can I cut from 3/4 of a metre of fabric looks difficult, but how many 75 mm squares can I cut from 750 mm looks much easier. Calculations often have to be mentally converted before they can be fed into a calculator. > I am using mm for my work because I'm working with parts less than 1000 m long > with tolerances ranging from 0.001 to 1 mm. This works out great, because I > never have more than 3 digits on either side of the decimal. Many dimension > ARE hard-metric to the nearest mm, so I don't waste my time working with 6 > digit numbers in these cases. This is what most people do within their workplace. They arrange for their units to provide convenient numerical values. Scientists and technicians will sometimes (often) create their own special (jargon) units for this purpose. I was often puzzled by the inability to communicate the idea of wool tenacity between wool combers and wool spinners, until I discovered that one lot were using newtons per kilotex as their unit and the other lot were using centinewtons per tex as theirs; one lot defined tex as grams per kilometre and the other lot defined it as milligrams per metre. As you and I know, it is only a matter of sliding decimal points backwards and forwards � but how far and how often do you have to do it is very important to those (such as textile mill workers) whose numerical skills are not well developed; to them kilotex and centinewtons are just incomprehensible jargon. I remember being profoundly impressed by some research done on the mathematical skills of adult Australians. This showed that slightly less than half of their subjects could readily (within a fixed time limit) add three items (such as $7.80, $13.25, and $11.90) from a restaurant luncheon menu. When they included the complexity of calculating a 10�% discount or 10�% tip (just slide the decimal point remember!) the number able to do this dropped to less than 10�%. > I would certainly not want to do landscape gardening in mm! A friend of mine is a landscape architect. I asked him what units he used and he replied that all of his drawings are done in metres or millimetres. When I asked why he replied, 'So all the tradesmen on the job can understand them and we never have to change from one lot of units to another. The large site layout drawings are done with the note, "All dimensions in metres" but anything that shows any detail has a note in the corner that says, "All dimensions in millimetres" and I have never seen anyone using centimetres'. To conclude, let me go back to your initial remark: > I still have a hard time accepting the general message that mm are always > preferable to cm. I don't think 'that millimetres are always preferable to centimetres'. For example, I do not doubt Marcus Berger's assertion that centimetres work well in Brasil. However, I have to wonder, based on my own experience, how long it took the Brasilians (from 1862) to make their metric transition. Did it take fifty weeks or did it take fifty years? I firmly believe that if you are planning a transition to metric and you want it to go relatively quickly and smoothly, then choose millimetres as your small unit. I commend to you these policy statements from the Australian building industry policy documents: �The SI units for linear measurement in building and construction will be the metre (m) and the millimetre (mm), with the kilometre (km) being used where required. This will apply to all sectors of the industry, and the centimetre (cm) shall not be used.� Standards Association of Australia, 1972, �Metric Handbook � Metric Conversion in Building and Construction � SAA MH1-1972� With these words the Australian Building and Construction Advisory Committee effectively banished centimetres from the building trades in Australia with the result that metric conversion in these trades was smooth, rapid, and complete. They made it clear that the centimetre should generally not be used, and in particular, "the centimetre should not be used in any calculation and it should never be written down" (op. cit.) Cheers, Pat Naughtin LCAMS Geelong, Australia Pat Naughtin is the editor of the free online newsletter, 'Metrication matters'. You can subscribe by sending an email containing the words subscribe Metrication matters to [EMAIL PROTECTED] --
