Experience the precision that built the modern world
Multiplication: Set first number on top scale, align with 1 on middle scale, find second number on top scale, read result below.
Division: Set dividend on middle scale under 1 on top scale, find divisor on top scale, read quotient on middle scale.
Pro tip: Click and drag the middle scale smoothly. The brass cursor shows your reading position!
Slide rules like this one were used by engineers to calculate the Apollo moon landing trajectories! These analog computers were the backbone of engineering from the 1600s to the 1970s, when electronic calculators finally took over. Every major engineering achievement - from skyscrapers to space missions - relied on the precision of these beautiful instruments.