British Thornton Slide Rule

Slide rule by British Thornton Ltd.

This is a slide rule, a sort of mechanical analogue calculating device, popular in the time before electronic calculators were developed. They were used particularly by engineers and scientists for doing complex calculations quickly.

The centre of the slide rule is a moving slider. The different parts of the slide rule are marked with a number of different scales that can be compared with each other. By moving the slider a certain number of places sideways and then comparing the numbers on the different scales, it is possible to do a range of calculations quickly, particularly multiplications and divisions.

This slide rule is fitted with a movable window with a cursor for reading off results more accurately, or for taking readings from other scales on the rule. This example dates from c.1967 – 1975 and was supplied by British Thornton, a Manchester-based supplier of drawing tools, mathematics instruments, and surveying equipment, which was originally established in 1880 as AG Thornton.