On 2008/12/27, at 12:16 PM, James Frysinger wrote:
You folks are squinting too hard.
Again, I think that this was never meant to be more than a rule of
thumb, a bit like "pi equals 22/7".
It's made a bit cuter by the fact that both a pint and a pound
contain 16 ounces, albeit different kinds of ounces.
Jim
Dear Jim,
I know that I'm wandering a bit off the track a bit here but the 22/7
approximation for pi was useful when we all had to trained to be
facile in handling fractions especially for the formula A = πr^2. In
what is now rapidly becoming a post-fraction more-decimal era, I find
the formula A = 0.8D^2 more convenient (where D is for diameter and
0.8 is an approximation for π/4 (more accurately 0.785 398)).
Let me give you an example. Outside of my office window I have a
rainwater tank that I know is close to 3 metres in diameter and 2
metres high to the bottom of the overflow pipe. I calculate its
capacity by squaring the diameter (3 m x 3 m = 9 m^2), multiplying
this cross section area by 0.8 (9 m^2 x 0.8 = 7.2 m^2), and then
multiplying by the height (7.2 m^2 x 2 m = 14.4 cubic metres). I would
probably round this down, to allow for the water I can't retrieve from
below the outlet tap, to 14 cubic metres and then think of the tank as
holding 14 000 litres.
My other rainwater tank is 1.8 metres wide and 2 metres high so I
figure that it holds close to 5000 litres.
Cheers,
Pat Naughtin
PO Box 305 Belmont 3216,
Geelong, Australia
Phone: 61 3 5241 2008
Metric system consultant, writer, and speaker, Pat Naughtin, has
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