Theodolite model known as a Ramsden theodolite, built by Nairne & Blunt. Mounted on four legs, one of which is fitted with a leveling screw. There are two telescopes. The upper telescope, which carries a bubble level, is adjustable vertically and horizontally. There are two scales for measuring its inclination. The second telescope was used to aim at a fixed reference point, ensuring that the instrument was always correctly oriented during the measurement operations. The orientation is also checked with a magnetic compass placed below the upper telescope. Provenance: Lorraine collections.