On Sat, Feb 25, 2006 at 01:02:39AM +1300, Russell McMahon wrote:
> > I made a bamboo slide rule for my dad last christmas, figured it was
> > fair as I have his one at my apartment. Still gotta learn how to use 
> > it
> > though.
> 
> Do it. takes about zero time to get the basics. Some advanced stuff 
> takes more effort or is easily forgotten. Being able to do simple 
> multiplication and division with pieces of wood or plastic gives 
> increased appreciation of the shoulders we are standing on.

Also been told some people like sliderules because it shows you the
relative magnitudes of the numbers you are working on at all times.

My dad once told me one of the earliest screw-ups he ever heard of with
an electronic calculator happened at the forestry department he was in.
Back in the mid 70's someone was off doing the calculations to see how
many trees they could sustainably cut in the university forest lot.
Aparently the calculations were done on an electronic calculator, and he
person doing them made a small error with the decimil points... A few
years later, in the early 80's, someone else noticed that they'd been
cutting ten times more trees than was sustainable. Ooops.

No word on whether the person who found the mistake was using a slide
rule though. :)

> The slide rule works by adding lengths of rule which are proportional 
> to the logarithms of the numbers being multiplied and reading off the 
> number whose logarithm is proportional to the resultant length. Far 
> easier to do than to explain.

Ahh, yeah, I remember the concept from highschool math, where even in my
time the teacher mentioned slide rules while teaching logorithms. I've
yet to actually get the details correct.

> Once you master that you can progress to measuring the heights of 
> doorways by dropping a coin and timing how long it takes to fall :-). 
> (Averaging 10 attempts produces almost usable accuracy).

Haha, yeah, gotta have a good stop watch though. I perfer Feynman's
(think this is where the story is from) methods, such as attaching a
long enough string and lowering the slide rule from the top of the
doorway... Or measuring the difference in period with a string and
sliderule pendulum and using the difference in gravitational field...

-- 
pete@petertodd.ca http://www.petertodd.ca
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