Azimuth compass. Engraved illustration of an early design of azimuth compass. This is designed to tell the angle between magnetic north and the Sun's position. The glass hemidome above the compass rose allows the inclusion of a vertical needle. This casts a shadow onto the rose from the Sun. At higher latitudes this can be used to determine the local magnetic variation (difference between true and magnetic north). This illustration was first published in the Gentleman's Magazine in 1754.