noun
A mechanical analog computing device used for multiplication, division, and other mathematical operations before electronic calculators became common.
祖父は計算尺を使って設計図を描いていた。
My grandfather used a slide rule to draw blueprints.
電卓 is an electronic calculator, while 計算尺 is a mechanical slide rule.
Compound of 計算 (calculation) and 尺 (ruler, scale).