Bisaker's slide rule, 1654, and Thacher's calculating instrument, 1881.
© Science Museum / Science & Society Picture Library
Bisaker's slide rule (bottom) is the earliest dated straight slide rule. The scales are mainly trigonometrical and logarithmic. The instrument is inscribed 'Made by Robert Bisaker, 1654, for TW'. Thacher's slide rule (top) is an extremely important American contribution to slide rules, capable of accurate reading to four decimal places.