Just as the Astra IIIB Deluxe sextant has become world famous as the premier low cost metal sextant, the Astra III Professional sextant with its low cost, high accuracy, and excellent handling qualities is destined to be the standard for professional seamen. Its construction is similar to the Tamaya sextants in that it has a bronze arc fused to an aluminum frame. The bronze arc can be manufactured to a higher tolerance than aluminum, which gives the sextant higher accuracy. At the same time the aluminum frame keeps the over-all weight low enough that fatigue is not a problem as with a solid bronze or brass sextant. Nevertheless, the additional weight of the bronze arc adds about 8 oz. and gives the instrument an excellent balance and “heft”.