Slide Rules

The slide rule's origins can be traced to the British mathematician Edmund Gunter (1581-1626). Gunter distinguished himself through the design of calculating devices, and was the first to use logarithmic scales for physical instruments.

He arranged logarithms into a scale, known as Gunter's line, which was then made into a two-foot rule with one side marked with logarithms and the other rulings for navigation (above) . By using a logarithmic scale to enable the conversion of multiplication and division into addition and subtraction, these rules were the predecessor of the slide rule. The example shown here was made by Robert Yeff in 1712, and was probably used as a general-purpose calculator at sea, where it would have been referred to simply as a "Gunter."

Read more: logarithms and their uses

Read more: the Gunter quadrant

The linear slide rule most recognised today gained popularity in the latter part of the 17th century.

It used a sliding piece of wood in a larger 'stock' with rulings on both pieces, with a cursor to align numbers.

For the first century of their existence, slide rules were typically crude and inaccurate, owing to the poor scale-dividing technology available. But as time went on, they became advanced and powerful tools for calculation.

The cylindrical slide rule shown here (Image 3) was developed in the late 19th century by E. Thacher, and had a scale that was 40 times greater than a standard linear rule, in addition to a magnifying glass for improved accuracy.

Thacher's model was just one of numerous new slide rule designs developed during the instrument's lifetime. Many were developed for use in specific tasks, such as calculations relating to brewing or the measurement of radiation doses.

Other designs purported to be 'universal' instruments, capable of solving numerous different types of numerical problem.