A late 18th-century ebony octant, stamped on the bone-ivory makers plate F. Walker 35 Wapping Wall, London, with double pin-hole sight, three shades, the brass index arm 9.5/8in. (24.5cm.) radius, with vernier, tangent-screw fine adjustment and clamp, with engraved plate signed B. Cole Sculp., in stepped keystone shaped oak case