Dear Bill and All, I have interspersed some remarks.
on 2003-03-22 06.14, Bill Potts at [EMAIL PROTECTED] wrote: > Terry Simpson wrote: >> [A] tidy up of the SI system would perhaps include abandoning prefixes that >> are not multiples of 1000. So we would no longer need the following >> prefixes: 'h', 'da', 'd' or 'c'. Thus we would only need to deal with one >> anomaly of lower case i.e. 'k'. > > The prefixes h and c are used with some very common and popular units. The > hectare is very useful in real-estate, including specifying the area of farms > and the planted area of individual crops within a farm. I agree that the hectare is useful, but it is its structure that worries me. It is the combination of a little used prefix 'hecto' and an obsolete unit 'are'. To my mind hectare is simply a slang or jargon word that is used as an abbreviation for either 'square hectometre' or for 10�000�square metres. > The hectopascal (hPa) > is useful in weather reports, as it is numerically the same as the familiar, > but obsolete, millibar. It is true that the hectopascal is used in some nations for air pressure reporting. However, in other nations (Canada?) the kilopascal is used. Can anyone tell us if use of the kilopascal in weather reports causes any problems. I believe that it is best in the long run to have only one unit for each quantity used in all nations � my preference is kilopascal. Do air pilots have an air pressure issue when they fly from a hectopascal region to a kilopascal region � or are they still flying with inches of mercury? > And, in spite of the acceptance of millimeters in construction (especially in > Australia, for example), and South Africa, New Zealand and many other nations who chose to use the smooth and rapid way to metrication of building construction. the centimeter remains an extremely useful unit. This is undoubtedly true in those nations where there has been enough time for a slow and confusing metrication process, using centimetres, to take place. It is my observation that metrication takes at least 50 years and, in many cases, longer if you choose to use centimetres as your small unit. > The cubic centimeter (cm2) is also very useful for specifying small enclosed > volumes (even though the milliliter variant of that unit is customarily used > where liquids are involved). Have you reinvented dry and liquid measures? Volume (dry) � cubic centimetres Volume (liquid) � millilitres > Elimination of the prefix d would also cause a problem. The formal definition > of the liter is 1 cubic decimeter (1 dm3). If d were eliminated, we could say > it was 1000 cubic centimeters (1000 cm3) -- in which case we couldn't > eliminate the prefix c. (We could hardly define the liter as 1000 mL. That > would be a tautology.) Or we could define the litre in terms of an SI unit � the cubic metre. 1 litre = 0.001 cubic metre > The elimination of da (for deca) might be possible. However, it wouldn't hurt > to keep it, even though it's rarely used. Maybe the prefixes, 'h', 'da', 'd' or 'c' will simply die out in time of their own accord and because of their disuse. Personally, I wouldn't encourage a campaign to get rid of these prefixes as I suspect that it would take a great deal of time and energy that would be best used to promote metrication in other ways. For example, I know that there are people who have a mindset that uses one or other of these prefixes regularly and no amount of time or energy will convince them to change that mindset. Cheers, Pat Naughtin LCAMS Geelong, Australia
