Just as the Astra IIIB has become world famous as the premier low cost metal sextant, the Astra III Professional Model 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”.
The handle is a new more comfortable design, and has an electrical outlet suitable for powering accessories. Except for the weight difference, accuracy, and handle improvement, it is exactly the same sextant as the basic Astra IIIB, and has all the attributes of it. These include thoroughly tested mirrors, maintainability, and the ability to quickly and economically change the horizon mirror type.
The sextant comes with a 3.5x40 telescope and wooden case as standard equipment. Optional items include a 7x35 telescope, zero magnification sight tube, a practice bubble horizon which facilitates effective back-yard practice without the need for a sea horizon, and a more expensive Professional Artificial Bubble Horizon. This provides a 2X power artificial horizon for use on land, or at sea if extremely calm conditions exist and the natural horizon is not visible. It connects to batteries in the handle for night lighting, and incorporates a dimming rheostat for use with faint stars.