The Mathematics of the Slide Rule – Logarithmic Computing

The slide rule was the engineer’s calculator from 1620 to 1972. It is based on logarithms: multiplication becomes addition of lengths on a logarithmic scale. The slide rule’s scales (C, D, A, B, K, etc.) allow multiplication, division, roots, powers, trig functions. The principle is log(a×b) = log a + log b. The slide rule has no battery and never breaks. It was used to design the first jetliners, the Apollo missions, and the atomic bomb. The electronic calculator killed it, but the slide rule remains a brilliant example of analog computation.