Three and a half inch travellers transit theodolite, c 1840.
© Science Museum / Science & Society Picture Library
Made by Robinson. The theodolite which measures vertical and horizontal angles is used in surveying. The origin of it is unknown but it has been traced back to 16th century English mathematician Leonard Digges. The theodolite has changed over time, in its current form it is a telescope mounted to swivel both horizontally and vertically. The theodolite is used to find angles in road building, tunnel alignment, and other civil-engineering work.