The Encyclopedia Americana (1920)/Slide-rule
SLIDE-RULE, an instrument for doing various mathematical operations in a mechanical way. It consists of two or more very accurately graduated and numbered pieces of wood or other material, one or more of which slides in a groove in the other. It may be flat or cylindrical. By shifting the movable slide or slides a variety of tedious arithmetical problems can be conveniently solved. It is almost indispensable to the draftsman and machine designer.