W. Stanley

“ We know that
square ( 25.4 ) must be a little larger than square ( 25 ) = 625 so that
it must be 646.0.
To extract a square root, we set the indicator over the number on the A
scale and read the result under the hair-line on the D scale. When we
examine the A scale we see that there are two places where any given
number may be set, so we must have some way of deciding in a given case
which half of the A scale to use. The rule is as follows:
(a) If the number is greater than one. For an odd number of digits to
the left of the decimal point, use the left-hand half of the A scale. ”

“ The process is called squaring the number. If we
find the number which, when multiplied by itself is equal to a given
number, the former number is called the square root of the given number.
The process is called extracting the square root of the number. Both
these processes may be carried out on the A and D scales of a slide
rule. For example:
Example 27: 4 * 4 = square ( 4 ) = 16
Set indicator over 4 on D scale. Read 16 on A scale under hair-line.
Example 28: square ( 25.4 ) = 646.0
The decimal point must be placed by mental survey. ”

“ A firm buys a typewriter with a list price of $150, subject to a
discount of 20% and 10%. How much does it pay?
A discount of 20% means 0.8 of the list price, and 10% more means
0.8 X 0.9 X 150 = 108. ”