ages of a slide rule.]

INSTRUCTIONS FOR USING A SLIDE RULE

The slide rule is a device for easily and quickly multiplying, dividing
and extracting square root and cube root. It will also perform any
combination of these processes. On this account, it is found extremely
useful by students and teachers in schools and colleges, by engineers,
architects, draftsmen, surveyors, chemists, and many others. Accountants
and clerks find it very helpful when approximate calculations must be
made rapidly. The operation of a slide rule is extremely easy, and it is
well worth while for anyone who is called upon to do much numerical
calculation to learn to use one. It is the purpose of this manual to
explain the operation in such a way that a person who has never before
used a slide rule may teach himself to do so.

DESCRIPTION OF SLIDE RULE

The slide rule consists of three parts (see figure 1). B is the body of
the rule and carries three scales marked A, D and K. S is the slider
which moves relative to the body and also carries three scales marked B,
CI and C. R is the runner or indicator and is marked in the center with
a hair-line. The scales A and B are identical and are used in problems
involving square root. Scales C and D are also identical and are used
for multiplication and division. Scale K is for finding cube root. Scale
CI, or C-inverse, is like scale C except that it is laid off from right
to left instead of from left to right. It is useful in problems
involving reciprocals.

MULTIPLICATION

We will start with a very simple example:

Example 1: 2 * 3 = 6

To prove this on the slide rule, move the slider so that the 1 at the
left-hand end of the C scale is directly over the large 2 on the D scale
(see figure 1). Then move the runner till the hair-line is over 3 on the
C scale. Read the answer, 6, on the D scale under the hair-line. Now,
let us consider a more complicated example:

Example 2: 2.12 * 3.16 = 6.70

As before, set the 1 at the left-hand end of the C scale, which we will
call the left-hand index of the C scale, over 2.12 on the D scale (See
figure 2). The hair-line of the runner is now placed over 3.16 on the C
scale and the answer, 6.70, read on the D scale.

METHOD OF MAKING SETTINGS

In order to understand just why 2.12 is set where it is (figure 2),
notice that the interval from 2 to 3 is divided into 10 large or major
divisions, each of which is, of course, equal to one-tenth (0