Before the more complex operations of involution, evolution, etc., are
considered, a few general hints on the use of the slide rule for
elementary operations may be of service, especially as these will serve
to enforce some of the more important points brought out in the
preceding sections.
Always use the slide rule in as _direct_ a light as possible.
Study the manner in which the scales are divided. Follow the graduations
of the C and D scales from 1 to 10, noting the values given by each
successive graduation and how these values change as we follow along to
the right. Do the same with the two halves of the A and B scales and
note the difference in the value of the subdivisions, due to the shorter
scale-lengths.
Practise reading values by setting 1 on C to some value on D and reading
under 2, 3, 4, etc., on C, checking the readings by mental arithmetic.
To the same end, find squares, square roots, etc., comparing the results
with the actual values as given in tables. Practise setting both slide
and cursor to values taken at random. Aim at accuracy; speed will come
with practice.
When in doubt as to any method of working, verify by making a simple
calculation of the same form.
Follow the orthodox methods of working until entirely confident in the
use of the instrument, and even then do not readily make a change. If
any altered procedure is adopted, first work a simple case and guard
carefully against unconsciously lapsing into the usual method during the
operation.
Unless the calculation is of a straightforward character, time taken in
considering how best to attack it (rearranging the expression if
desirable) is generally time well spent.
In setting two values together, set the cursor to one of them on the
rule, and bring the other, on the slide, to the cursor line.
In multiplying factors, as 57 × 0·1256, take the fractional value first.
It is easier to set 1 on C to 1256 on D and read under 57 on C, than to
reverse the procedure. When both values are eye-estimated, set the
cursor to the second factor on C and read the result on D, under the
cursor line.
In continuous operations avoid moving the slide further than necessary,
by taking the factors in that order which will keep the scale readings
as close together as possible.