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. The hectopascal (hPa) is useful in weather reports, as it is numerically the same as the familiar, but obsolete, millibar. And, in spite of the acceptance of millimeters in construction (especially in Australia, for example), the centimeter remains an extremely useful 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). 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.) The elimination of da (for deca) might be possible. However, it wouldn't hurt to keep it, even though it's rarely used. Bill Potts, CMS Roseville, CA http://metric1.org [SI Navigator]
