slide rule

American  

noun

1. a device for performing mathematical calculations, consisting essentially of a ruler having a sliding piece moving along it, both marked with graduated, usually logarithmic, scales: now largely replaced by the electronic calculator.

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slide rule British  

noun

1. 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

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Etymology

Origin of slide rule

1655–65 for earlier sense; 1875–80 for current sense