The devices compute the integral or circumference of a drawn curve, when the pointer at the end is moved along the curve. More pictures to help unravel the mystery of its operation. A slide rule has graduations on logarithmic scales, so that the catenation of two factors gives the product.
Serial calculation is easy, and trigonometric functions are also available.
With care 3-digit accuracy can be obtained. Table of Integrals, Logarithms, and Functions. Manual or electric calculators, as shown on the first floor , were used together with mathematical tables for scientific computation. A group of 12 computors , working in pairs for cross-checking, took up to three weeks to obtain one result.