"Gilligan" wrote in message
. ..

"Edgar" wrote in message
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"Gilligan" wrote in message
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"Edgar" wrote in message
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Rule of Thumb does not normally call for a knowledge of calculus...



Here are some rules of thumb for the applications of integrals in
calculus:

http://www.math.hawaii.edu/~lee/calculus/Integrals.html

Is this abnormal?

No, I would say it is normal. His 'rules of thumb' are directed at
people
who have not yet, or do not need, to learn the theories in their
entirety,
and he admits that they do contain inaccuracies.
That is exactly what a 'rule of thumb' is- a shortcut for everyday use
for
those who do not wish, or are unable, to get too deeply involved in the
basic theorems.

Rules of thumb might even be useful for those highly skilled in the art
who
wish to reach a quick, back of the envelope solution.

Yes, indeed. It does not make sense to calculate something to many places of
decimals when the input data is not in itself all that accurate. If you do
that you are just deluding yourself.
The best rule of thumb I can think of off the top of my head is the rule of
12ths for calculating tidal heights. Works pretty well on the whole for
practical purposes but ignores barometric pressure effects and is not valid
for ports such as the Solent in Uk that have special tidal effects.
I used it to good effect once in the port of Treguier in France. There is up
to 30 feet tidal range there. The tide was starting to fall and several of
us were anchored lower down the river eyeing the last good place to anchor
nearer the town. It was clear all were wondering if they would find
themselves aground at low water. I used the 12ths rule and decided to go for
it and it worked for me as at low water I had 1 foot below my keel. Everyone
else had a long trip in the dinghy!