Navigational instruments designed by the Englishman John Davis in 1594. This instrument measures the height of the sun by the projection of a shadow. In this case the observer stands with their back to the sun, hence the English name 'backstaff'. Instead of the cross of the Jacob's staff, the Davis quadrant features two arcs to which sliding vanes are mounted. By taking the horizon as the starting point, the observer can measure the shadow of the vane on the first arc using that of the second arc. The Davis quadrant was originally made of wood with ebony or ivory quadrants.Brass or steel predominanted after about 1775.
