tal multiplication. Thus, in example 3a above, we
can multiply 2 by 7 in our heads and see immediately that the decimal
point must be placed in the slide rule result 156 so that it becomes
15.6 which is nearest to 14. In example 3b (20 * 7 = 140), so we must
place the decimal point to give 156. The reader can readily verify the
other examples in the same way.

Since the product of a number by a second number is the same as the
product of the second by the first, it makes no difference which of the
two numbers is set first on the slide rule. Thus, an alternative way of
working example 2 would be to set the left-hand index of the C scale
over 3.16 on the D scale and move the runner to 2.12 on the C scale and
read the answer under the hair-line on the D scale.

The A and B scales are made up of two identical halves each of which is
very similar to the C and D scales. Multiplication can also be carried
out on either half of the A and B scales exactly as it is done on the C
and D scales. However, since the A and B scales are only half as long as
the C and D scales, the accuracy is not as good. It is sometimes
convenient to multiply on the A and B scales in more complicated
problems as we shall see later on.

A group of examples follow which cover all the possible combination of
settings which can arise in the multiplication of two numbers.

Example
4: 20 * 3 = 60
5: 85 * 2 = 170
6: 45 * 35 = 1575
7: 151 * 42 = 6342
8: 6.5 * 15 = 97.5
9: .34 * .08 = .0272
10: 75 * 26 = 1950
11: .00054 * 1.4 = .000756
12: 11.1 * 2.7 = 29.97
13: 1.01 * 54 = 54.5
14: 3.14 * 25 = 78.5

DIVISION

Since multiplication and division are inverse processes, division on a
slide rule is done by making the same settings as for multiplication,
but in reverse order. Suppose we have the example:

Example 15: (6.70 / 2.12) = 3.16

Set indicator over the dividend 6.70 on the D scale. Move the slider
until the divisor 2.12 on the C scale is under the hair-line. Then read
the result on the D scale under the left-hand index of the C scale. As
in multiplication, the decimal point must be placed by a separate
process. Make all the digits except the first in both dividend and
divisor equal zero and mentally divide the resulting numbers. Place the
decimal point in the slide rule result so that it is nearest to the
mental result. In example 15, we mentally divide 6 by 2. Then we place
the decimal point in the slide rule result 316 s