The Earliest Surviving Dated Astrolabe – An astronomical instrument used for observing planetary movements, was indispensable for navigation. A type of analog calculator, brass astrolabes were developed by mathematicians in the medieval Islamic world.
Muhammad ibn Abi Bakr al Ibari century) Astrolabe with geared calendar, Oxford, Museum of the History of Science. Of Persian origin, and one of the oldest complete devices of it's like in the museums collection.
Astrolab (dated century): This was for measuring the altitude of heavenly bodies above the horizon, and so determining (among other things) the time of day or night. Readings are taken by means of rotatable alidade, a diametrical rule with sights.
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