Wooden backstaff or Davis quadrant made by John Gilbert on Tower Hill, London, England in 1730 for Thomas Wells. The navigational instrument is fitted with boxwood circular scales (30°arc 0-25, 60°arc 0-65 & 0.5’ divisions), signed ivory insert and decorative stars are stamped on the frame and arcs. The backstaff is fitted with a replacement Flamsteed Lens and a shadow vane made in the Science Museum workshops in 1967 (copied from Inv. No.1908-158).