about slide So let us launch

Found at: sdf.org:70/users/melton/phlog/slide-rule-revisited

The Slide Rule and the neighborhood

about slide rules.  So let us launch into another problem involving
than punching the numbers in on the calculator.

Our man is standing atop a 300 ft. ocean front cliff and observes a
We'll refer back to our handy table for solutions to right
triangles.  There are a couple of approaches we can take, but in
this case since we are given the angle of depression, we'll subtract
that from 90° to give us our remaining angle which is 78°.
To determine the distance from the base of the cliff to the boat
(we'll call it 'a'), we multiply 300 * (TAN 78°) = a.  So first
let us find the tangent of 78° on the slide rule.  Hmm...the
tangent scale only goes from 5.7° to 45°.  Let us see what
one of my slide rules (Sterling Acumath 400) provides a solution:

So if we follow this path then 90°-78°=12°.  Back to

Now we need the reciprocal of .212.  Here we go to the 'CI' and 'D'

To determine the decimal point when finding reciprocals one of the

To find y = 1/x:

- Convert x to scientific notation and read it's coefficient c and
t's exponent, p
- if the coefficient is 1 or -1 exactly, y exponent is -p
- otherwise y's exponent is -p-1

To get our decimal in the correct place, we convert .212 to
Acumath slide rule the 'CI' scale is on the slide.  We place the
cursor over 2.12 on the CI scale (remembering the 'CI' scale
ncreases from right to left) and read down to the 'D' scale which
neither 1 or -1, the exponent of our answer is -(-1)-1 = 0 so our

t out.  Now we multiply the height of the cliff (300 or 3E2) times
the tangent of 78° which we just figured out is 4.71E0.  On the
the 'D' scale:

Then we move the cursor over to 4.71E0 on the 'C' scale and read our
answer directly below on the 'D' scale, in this case, 1.42.  

Now we add the exponents 0 + 2 = 2, but since we have to adjust for
the change of magnitude (3 * 4.71 > 10), We add one to the exponent
(0 + 2 + 1 = 3).  Our answer is 1.42E3 or 1420.  What does the
calculator tell us?

and calibration.  The additional factor is the user's ability to set
t and read the values.  For most applications, three significant
figures is good enough.

Now that we have gone through this seemingly tedious exercise, I am
the mathematical equivalent to stopping and smelling the roses.  In
our rush for an instant answer or instant gratification, we miss out
on the intimate details of the journey.  In a similar way, it is
like the difference between hopping in our car and driving to the
local market for our groceries, or slowing down and taking the
bicycle or even walking and have more intimate contact with the
neighborhood and surroundings.  As I have mentioned in a previous

a simple tool like the scythe allows one not only to mow grass and
ntimate with the subtleties of the land (and wildlife) that would
otherwise be lost when sitting in a tractor noisily masticating the
on a journey to an answer and on the trip, we become more familiar
the Luddites only destroyed machines that did not support or foster
the "commonality."  Sometimes I find myself pausing and reflecting
f a particular technology I am using meets that standard, or have I
become a slave to that particular device and all of its ancillary