RE: [SI-LIST] : What's your favorite Screwy SI Concept?

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From: Richard A. Schumacher ([email protected])
Date: Tue Jan 11 2000 - 16:55:06 PST

> A word on rules of thumb... We all use rules of thumb every day in our
> work and daily lives. These come from many sources and we cannot
> possibly check them all out. For instance, Henry Ott's book is full of
> rules of thumb and summaries of principles such as the equation for
> radiation from a hole. Henry's book would have to be VERY long to
> provide the proof of all of them. But, they are reasonable and come from
> a knowledgeable source so we use them. Sometimes we misapply a principle
> here or there but for the most part such an approach works (or we would
> all be looking for work OR get very little sleep trying to check out
> everything we read). If a rule of thumb makes sense given one's own
> knowledge and experience and it comes from a reliable source, use it. It
> is always good to generate our own data or proof on these matters, but
> that is not always practical. Isn't this characteristic, that of
> building on the work of others involving some trust, what distinguishes
> human beings from animals, the ability to pass on information without
> each generation having to continually regenerate it for themselves?

All true. But note that this works only when the chain of attribution
ends either in a reference to a detailed description of a demonstration,
or a mathematical proof, or with a statement by a trusted authority.
The problem with some of these rules of thumb is that they root from
statements by some guys most of us never heard of, with no supporting
experimental data and no convincing theoretical argument.

> What really makes this work was said by Carl Sagan:
> ~"A good engineer or scientist must be willing to drop their most
> cherished theories in the face of credible evidence to the contrary."

Exactly. When rules of thumb conflict with what we think we know
we (correctly) require credible evidence of their applicability
before we accept them. My fondest wish is that my employer's
competitors accept and use all the rules of thumb they find :_>

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