Slide rules were commonly used prior to the invention of the calculator. The Slide rule was used for performing multiplication, division and other scientific functions up through the 1960s and prior to the development of the electronic calculator. Used by Frank Smythe, engineer. Used up to the 1960's prior to the invention of the electronic calculator. Metal rule, hard cardboard case. The slide rule consists of two divided scales, one fixed and one movable, and a sliding window called a cursor. The Slide rule was used for performing multiplication, division and other scientific functions up through the 1960s and the development of the electronic calculator. System Darmstadt dmake, sun Hemm, Japan. "F. SMYTH" is annotated on the slide rule cover. slide rule, circa 1950 slide rule, trade measurements and calculations slide rule