A cross-staff, c. 1700.

Cross-staff.

Repro ID: D0423

Description: The cross-staff was a device for measuring the altitude of the sun or Pole Star. It made use of the properties of right-angled triangles, or trigonometry. The observer rested the main staff on the bone just below his eye and moved the cross until the bottom was in line with the horizon, and the top with the lower limb (edge) of the star or sun, he then read off the position on the scale in degrees and minutes. Cross-staves were normally made of wood and few have survived.

Creator: Thomas Tuttell

Date: c. 1700

Credit line: National Maritime Museum, London