This is a superb post by our colleague, Tom. Very little could be added to it. Nonetheless, I'd like to add my voice to his and provide additional insights on a few parts below. BTW, thanks, Tom, for a very insightful post.
On Thu, 09 Jan 2003 09:18:59 Tom Wade VMS Systems wrote: ... >1. One of the disadvantages of having a single unit (of length for example) >is that a convenient size for measuring one set of objects is not suitable >for another... > I have to echo his opinion above. Well said! I'd go even further to say that maybe we may be missing at least a couple of new prefixes which could be handy for a few applications, the 10 to 4 and 10 to -4. But getting BIPM to agree on the creation of these has already proven to be a pain... >Unlike the Imperial/Colonial systems, the subunits can be readily converted >by inspection, which is a huge disadvantage of these older systems. > Only a small remark to say that I don't particularly like the use of the word 'conversion' when referring to navigation between prefixes. Simply because technically prefixes are *mathematical entities* COMPLETELY dissociated from the unit they're being applied to. Therefore, there is actually no conversion taking place per se but rather a rearrangement/relocation of a decimal point. >So if you remove some prefixes, you put the metric system at a disadvantage >because of the relative inconvenient size of the resultant units, which is >not in our interests. > Indeed, I think we should all agree with this. > >2. If any of these rare units are in regular use, then not teaching the full >range will mean someone will eventually stumble over one of the unlearned >ones, e.g. decibels, dekanewtons, hectopascal et, and conclude that the >metric system has exceptions and contradictions of its own. > That's a very valid concern. >3. In teaching, it is important to stress the consistent way in which the >metric system is put together. All the different quantities have the same >range of prefixes, and they go up (or down) in 10s as far as the thousand (or >thousandth) and in thousands thereafter. Otherwise you have 'holes', and one >of the beauties of the metric system is lost... > >Keep it simple and consistent. > Agreed. And if my suggested addition of new prefixes ever occur I'd not consider them as necessarily 'inconsistent' or unduly 'complex'. The SI system must do its best to satisfy the needs of users. ... >However, this does not mean that cm shouldn't be used outside such a group, or >that cm should be ignored in teaching the metric system. When it comes to >measuring people's height, the cm is much more convenient than the mm, as >height is rarely measured to that exactitude, and you therefore have a >superfluous digit. Just a small remark to mention that what's really important for us to realize in the above example is the *accuracy* requirement for such measurements. That's what actually settles the question. One simply canNOT use heights to the mm precision since people's heights do vary depending on the hour of the day. The maximum one can expect is use half a centimeter when reporting it. But even that may be overkill. On the other hand, one should also not forget the basic principle of when the unity is reached, especially when that is the fundamental base unit, like the meter. One should give preference to stating the measured value with that format. I.e. 1.74 m should be preferred over 174 cm! I honestly can't buy this whole notion of avoiding decimal points like the plague. If the population is never bothered by the presence of cents in their daily monetary dealings why should they be when facing body measurements??? ... >[Aside: I note that someone claimed that the Australian clothing industry's >failure to metricate when compared to building was due to the former's use of >cm and the latter's use of mm. This would be a more convincing argument if >they could cite a successful migration of a clothing industry elsewhere using >mm. I believe that cm are quite suitable (no pun intended) for clothing, and >the relative failure is due to other factors such as greater familiarity of the >public with legacy units when dealing with body dimensions (even in AU, some >people still quote height in feet and inches).] > Indeed, I find it compelling to agree with Tom on the above. Again, it goes to *accuracy* and usage, deriving measurements and sizes of clothes to the mm accuracy is IMHO overkill. Trying to use mm here is akin to trying to transform this particular prefixed unit (sorry, Gene) into a universal standard one when that would be utterly unnecessary and perhaps even a hindrance due to its potentially large number of digits to handle. Again, folks, we should remember the good old principles learned at school that we can only present a measurement to a specific accuracy when that can be measured, first of all, and when that is relevant! ... >So please, stop treating hecto, deka etc as something to be swept under the >carpet. If they are not a convenient unit for your purpose, fine, don't >use them, but they are just as valid as kilo and milli, and may be more >appropriate for other people. > Finally, I feel I should add my voice to Tom's here, once again. We've got better fish to fry than to waste our times on discussions like these (MHO!...). Marcus ____________________________________________________________ Get 25MB of email storage with Lycos Mail Plus! Sign up today -- http://www.mail.lycos.com/brandPage.shtml?pageId=plus
