A mechanical device consisting of a sliding portion and a fixed case, each marked with logarithmic axes. By lining up the ticks, it is possible to do multiplication
by taking advantage of the additive property of logarithms.
More complicated slide rules also allow the extraction of roots and computation of
trigonometric functions.

According to Steinhaus (1999, p. 301), the principle of the slide rule was first enumerated by E. Gunter in 1623, and in 1671, S. Partridge constructed an instrument similar to the modern slide rule. The Oughtred Society, a group of slide rule collectors, claims that W. Oughtred invented the first slide rule in 1622.

The slide rule was an indispensable tool for scientists and engineers through the 1960s, but the development of the desk calculator (and subsequently pocket calculator) rendered slide rules largely obsolete beginning in the early 1970s.

Electronic Teaching Laboratories. Simplify Math: Learn to Use the Slide Rule. New Augusta, IN: Editors and Engineers, 1966.Johnson,
L. H. The
Slide Rule. New York: Van Nostrand, 1949.Oughtred Society. "Slide
Rule History." http://www.oughtred.org/history-new.shtml.Saffold,
R. The
Slide Rule. Garden City, NY: Doubleday, 1962.Steinhaus, H. Mathematical
Snapshots, 3rd ed. New York: Dover, pp. 91-92 and 301, 1999.