RE: [MLUG - DISCUSSION] beginner slide rule wanted

[Jonathan King <EMAIL:PROTECTED>]

On Wed, 2 Jul 2003, Matthew Ross wrote:

> > > If you do happen to find someone locally selling one of the 20"
> > > behemoths for a reasonable price, let me know. While it's not very
> > > useful in a practical sense (no graph mode on a slide 
> > > rule), it is very intimidating in a meeting to use a slipstick to do your 
> > > calculations.
> > 
> > Really?  Isn't it slower and less accurate than a handheld calculator?  It
> > wouldn't scare me much!
> 
> The slide rule is a glorified multiplication table, log table, exponent
> table, etc. The bulk of the calculations are done in your head, and the
> only interaction with the slide rule is to get a number when one doesn't
> readily pop from your head.

OK, so not to enter a flame war about this...but I feel you're both 
missing a bit of something.  Back in the days when people did routinely 
learn to use a slide rule, if you found somebody who could use one *well*, 
you had almost certainly bumped into somebody who had good problem-solving 
skills and a fairly deep sense about how numbers and numerical computation 
worked.  People like that really could do impressive work with one. (Also 
see below.)

The problem, of course, is that while a slide rule is a pretty marvelous
instrument, there were some inherent practical limitations.  So the number
of sig figs you could extract from an answer was always an issue;  
programmability just didn't exist; the number of scales on a rule tended
to get quite high, which limited its usefulness for more basic problems,
etc. All of these are reasons why slide rules went away, and they do still
apply.

Now, the intimidating thing about an expert slide rule user wasn't that
they could whip out an answer quickly on a 20" slip stick, but that when
asked to do a calculation the response would often go like this: "OK, so
that should be close to .0477...[slide, slide, read off rule]...and the
stick says .0479." Now, even a 70s era caculator could spit back something 
more accurate (say .04788594), and just as quickly, but you wouldn't 
necessarily get the sense that the calculator user had the same feeling 
for the problem, or would recognize if the answer were wrong (because a 
wrong key was hit).  To be an effective slide rule user, you tended to 
have excellent estimation skills, since you had to recognize major 
screw-ups.

Now, the people who leapt from slide rules to the (then expensive)
calculator were in really great shape, since they were good estimators who
*immediately* benefitted from having 8 sig figs.  So the University of
Texas used to have a famous annual slide rule contest, but they quit in
1975 since the experts had embraced the calculator, and the slide rule 
no longer ruled in any way.

Now, if you fast forward to 2003, it's clear that we're not in such great 
shape anymore.  Nobody really knows much about estimation or back of the 
envelope calculation, so there are way too many people who can give you 8 
sig figs of nonsense and not have any clue what happened.  And then you 
take away their calculator, and they are toast.

So every year I walk students through the Tower of Hanoi Problem with a
small number of disks, establish that the number of moves it takes for the
n disk problem is 2^n - 1, and then ask for people to guess how long the
64 disk problem takes if you can do 1 move per second.  The modal guess is
usually off by a factor of 50 billion or so.  I submit that an error
anywhere near this large would never happen to anybody who knew how to use
a slide rule.

That's not to say that I think a slide rule is the only way to learn about 
how to do stuff like this, just that it is *a* way, and it's not clear to 
me that many better ways have come down the pike since the 70s.

OK, I'm done. :-)

jking


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