slide rule

n. a thin, flat calculating device consisting of a fixed outer piece and a movable middle piece. Both pieces are graduated in such a way (as, by a logarithmic scale) that multiplication, division, and other mathematical functions of an input variable may be rapidly determined by movement of the middle pieces to a location on one scale corresponding to the input value, and reading off the result on another scale. A movable window with a hairline assists in alignment of the scales. This device has been largely superseded by the electronic calculator, which has a greater precision than the slide rule. Also called colloquially slipstick. [ PJC ]