An ivory staff and four decoratively engraved ivory vanes. The sky-end of the staff is pyramid-shaped. The vanes are in two parts and are held together by brass pins. The fourth vane has a fixed ivory horizon. The beginnings of the scales on all four sides are marked ‘Altitude’, and ‘Complement’ for the zenith distance.

The scales are from 90° to 34° (side one); from 90° to 20° (side two); from 90° to 10° (side three) and from 90° to 4° (side four), this is vice versa for the zenith distance. The maximum reading accuracy is 10 arcminutes for the sides one to three, and 5 arcminutes for side four.

Signed on side one: ‘Thomas Tuttell Charing + Londini fecit’
Signed on side two: ‘Fait par Tho: Tuttell Ingenieur de sa MAIESTÉ BRITANIQUE | pour les Instruments Mathemathiques á LONDRES’.

Cross-staves were normally made of wood and few have survived. The cross staff was probably not meant for use on board a ship. It was part of a presentation set including a backstaff (NAV0040), two Gunter’s scales (NAV0108 and NAV0107), and a sector (NAV0166), all fitting in a lyre case. The inscription may point towards an original French owner.