Should we be talking about the rule of 1000 or the rule of 10^(NM) where N is the power of the unit concerned and M is an integer of our choice. In most cases = 1, so we can set M = 3.
In the case of volumes, N = 3, so if we set M =1, we still get to the rule of 1000. However in the case of areas, N = 2, so the rule of 1000 is not possible. If we set M = 2, we get large steps and we also loose out on the rule of 1000². If however we set M = 1, then we have smaller steps, but we can still use the rule of 1000². This suggests that areas should be mm², cm², dm², m², a, ha, km² etc. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Pierre Abbat Sent: 06 February 2009 16:02 To: U.S. Metric Association Subject: [USMA:42896] Re: ectare was: An Associated Press article On Friday 06 February 2009 08:20:05 Jon Saxton wrote: > I respectfully disagree. > > There is a fundamental problem with the "rule of 1000" when applied to > powers of units. "Rule of 1000" becomes "rule of 1 000 000" for area and > "rule of 1 000 000 000" for volume so it is fairly obvious that we need > some intermediate units for common sizes. The litre/liter for volume is a > good example. > > The hectare works for land and is easy to visualise (100 m x 100 m). > Whether 10 x100 or 20 x 50 is easier or harder is incidental. Area is > actually more problematic than volume because we like to think in squares > and 1000 is not a square. Or 40×25 or 31.25×32. 40×25 is approximately a common lot size in residential subdivisions. I'm doing a subdivision in my class where the lots are a little smaller than that. > What do you think would be a good unit for measuring the area of video > screens? mm² is too small for your television and m² impractical for your > iPod. Even cm² is probably too small for TV screens. A practical unit > might be dm² - that would give screen sizes in the range 0.2 dm² to 200 dm² > for the most part. That's 2 microdunams to 2000 microdunams. Does that sound like a good range to you? > In the case of area you have to abandon one concept or the other. If you > want neat squares for area then the rule of 1000 has to be replaced by a > rule of 100. If you want to adhere religiously to the rule of 1000 then > you have to give up square units of area. I prefer keeping the powers of 1000, as they're easier to calculate with. Agricultors have been dividing yield by area since ancient Egyptian times; the Rosetta Stone has a figure in ardebs per arura. Do you know anyone from the eastern Mediterranean countries where they actually use the dunam? Do they find them easier to calculate with? Pierre
