Pat, I defer to your experience. Logic alone is no substitute for a well executed experiment.
John On Wednesday 05 November 2003 04:17, Pat Naughtin wrote: > 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] > --
