The slide rule may be defined as an instrument for mechanically
effecting calculations by logarithms. Those familiar with logarithms and
their use will recognise that the slide rule provides what is in effect
a concisely arranged table of logarithms, together with a simple and
convenient means for adding and subtracting any selected values. Those,
however, who have no acquaintance with logarithms will find that only an
elementary knowledge of the subject is necessary to enable them to make
full use of the slide rule. It is true that for simple slide-rule
operations, as multiplication and division, a knowledge of logarithms is
unnecessary; indeed, many who have no conscious understanding of
logarithms make good use of the instrument. But this involves a blind
reliance upon rules without an appreciation of their origin or
limitations, and this, in turn, engenders a want of confidence in the
results of any but the simplest operations, and prevents the fullest use
being made of the instrument. For this reason a brief, but probably
sufficient _résumé_ of the principles of logarithmic calculation will be
given. Those desiring a more detailed explanation are referred to the
writer’s “Logarithms for Beginners.”
The slide rule enables various arithmetical, algebraical and
trigonometrical processes to be performed with ease and rapidity, and
with sufficient accuracy for most practical purposes. A grasp of the
simple fundamental principles which underlie its operation, together
with a little patient practice, are all that are necessary to acquire
facility in using the instrument, and few who have become proficient in
this system of calculating would willingly revert to the laborious
arithmetical processes.