sighting slit

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• Backstaff — Not to be confused with Ballastella. Davis quadrant from the beginning of the 18th century The backstaff or back quadrant is a navigational instrument that was used to measure the altitude of a celestial body, in particular the sun or moon. When… …   Wikipedia

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• Alidade — An alidade (archaic forms include alhidade, alhidad, alidad) is a device that allows one to sight a distant object and use the line of sight to perform a task. This task can be, for example, to draw a line on a plane table in the direction of the …   Wikipedia

• Almucantar — An Almucantar, also spelled almucantarat or almacantara, is a circle on the celestial sphere parallel to the horizon. Two stars that lie the same almucantar have the same altitude.Almucantar staffAn almucantar staff is an instrument chiefly used… …   Wikipedia

• Quadrant (instrument) — Ptolemy using a quadrant A quadrant is an instrument that is used to measure angles up to 90°. It was originally proposed by Ptolemy as a better kind of astrolabe.[1] Several different variations of the instrument were later produced by medieval… …   Wikipedia

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• Conning tower — A conning tower is a raised platform on a ship or submarine, often armored, from which an officer can con the vessel; i.e., give directions to the helmsman. It is usually located as high on the ship as practical, to give the conning team good… …   Wikipedia

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