Theodolite, 18th century.
© Science Museum / Science & Society Picture Library
This instrument by Benjamin Cole bears the coat of arms of the Duke of Cumberland, and may have been used by him on the survey of the Highlands of Scotland in 1747. It measures both vertical and horizontal angles, a type of theodolite not widely used by ordinary surveyors until the 19th century. The horizontal angle between two positions was read off the base while vertical angles were read off the arc. It would have stood on a tripod.