e numerator. Since two
is out beyond the body of the rule, transfer the slider till the other
(left-hand) index of the C scale is under the hair-line, and then move
the indicator to 2 on the C scale. Thus, successive division and
multiplication is continued until all the factors have been used. The
order in which the factors are taken does not affect the result. With a
little practice you will learn to take them in the order which will
require the fewest settings. The following examples are for practice:

Example 56: (6/3.5) * (4/5) * (3.5/2.4) * (2.8/7) = .8

Example 57: 352 * (273/254) * (760/768) = 374

An alternative method of doing these examples is to proceed exactly as
though you were multiplying all the factors together, except that
whenever you come to a number in the denominator you use the CI scale
instead of the C scale. The reader is advised to practice both methods
and use whichever one he likes best.

3. The area of a circle. The area of a circle is found by multiplying
3.1416=PI by the square of the radius or by one-quarter the square of
the diameter

Formula: A = PI * square( R )
A = PI * ( square( D ) / 4 )

Example 58: The radius of a circle is 0.25 inches; find its area.

Area = PI * square(0.25) = 0.196 square inches.

Set left-hand index of C scale over 0.25 on D scale. square(0.25) now
appears above the left-hand index of the B scale. This can be multiplied
by PI by moving the indicator to PI on the B scale and reading the
answer .196 on the A scale. This is an example where it is convenient to
multiply with the A and B scales.

Example 59: The diameter of a circle is 8.1 feet. What is its area?

Area = (PI / 4) * square(8.1)
= .7854 * square(8.1)
= 51.7 sq. inches.

Set right-hand index of the C scale over 8.1 on the D scale. Move the
indicator till hair-line is over .7854 (the special long mark near 8) at
the right hand of the B scale. Read the answer under the hair-line on
the A scale. Another way of finding the area of a circle is to set 7854
on the B scale to one of the indices of the A scale, and read the area
from the B scale directly above the given diameter on the D scale.

4. The circumference of a circle. Set the index of the B scale to the
diameter and read the answer on the A scale opposite PI on the B scale

Formula: C = PI * D
C = 2 * PI * R

Example 60: The diameter of a circle is 1.54 inches, what is its
circumference?

Set the le