Mariner's or altitude quadrant

This is a simple instrument of Portuguese or Spanish origin, used in navigation from the mid-15th to 17th centuries, to calculate latitude. It consists of a quarter-circle panel of wood, graduated from 0º to 90º on a brass dial. Along one edge there are two sights, and a plumb line hangs from the center of the quadrant. When aimed at the sun, through the sights, the line would indicate the sun's altitude on the horizon on the quadrant's graduations. This specific example is a reproduction from 1982 by Juan San Martín Buceta.