R. I. Nelson wrote:

> This has to be a different meaning in different country thing.  I n all 
> school, college and military classes I have taken the word EXACT  means 
> right on no variance one way or the other.  To my knowledge engineering 
> is supposed to be an "exact science". Not a half way thing of "that 
> looks close enough".

Mathematics (and logic) is the only thing that's exact, and it's neither
science nor engineering. I'd go so far as to say that there's /nothing/
exact in engineering (and that goes for every country I know :). Every
measurement has a tolerance range around it, and not even that range is
exact, as it's usually just a short hand notation for a not quite well
known probability distribution around the given value.

In science and engineering classes, IMO, should be taught that e.g. 6 V
doesn't really say much, it needs to be e.g. (6 +-0.2) V to make sense.
Because for example (6 +-0.00001) V is something quite different -- and
even that's pretty close to "right on" or "exact" or "no variance", it's
obviously none of these. I've never seen a measurement that was 6 V
/exact/, in the sense of (6 +-0) V. And, you may find that ironic (but it's
actually quite obvious), the more you get into high precision work, the
more important become the tolerances. They are left out (and as such are
implied to be low precision) only in low precision situations; everywhere
precision is relevant they always use values with tolerances. 

I don't know whether you have done engineering work for other people. One
of the most common phrases one hears is "that's close enough" (or maybe
"that's too expensive, make it simpler" :). We (almost) never do the best
we could do given unlimited funds and time, we pretty much always do it
"good enough" and "as simple/cheap/quick as possible". Nothing "exact" or
"precise", all a matter of trade-offs, a lot of "half way things". Having a
good feeling for the "right" trade-off is basically what engineering is
about... :)

Now I don't know much about the military. Maybe they operate in a different
universe :)

Gerhard

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