Slide rule | mathematics
Slide rule, a device consisting of graduated scales capable of relative movement, by means of which simple calculations may be carried out mechanically. Typical slide rules contain scales for multiplying, dividing, and extracting square roots, and some also contain scales for calculating trigonometric functions and logarithms. The slide rule remained an essential tool in science and engineering and was widely used in business and industry until it was superseded by the portable electronic calculator late in the 20th century. The logarithmic slide rule is a compact device for rapidly performin...
Source: britannica.com