# about slide So let us launch

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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