A slide rule is an instrument that you use for calculating numbers. It looks like a ruler and has a middle part that slides backwards and forwards.
slide rule in British English
noun obsolete
a mechanical calculating device consisting of two strips, one sliding along a central groove in the other, each strip graduated in two or more logarithmic scales of numbers, trigonometric functions, etc. It employs the same principles as logarithm tables
slide rule in American English
a mechanical mathematical device consisting of a ruler with a central sliding piece, both parts being marked with various number scales: used to find square roots, logarithms, quotients, etc. rapidly
Examples of 'slide rule' in a sentence
slide rule
Hall took a round pilot's slide rule from the seat's side pocket and turned the bezel with his thumb.
Lunnon-Wood, Mike LET NOT THE DEEP (2003)
He thought about that so hard I was surprised he didn't take out a slide rule.