Mariner's astrolabe
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The mariner's astrolabe, also called sea astrolabe, was an inclinometer used to determine the latitude of a ship at sea by measuring the sun's noon altitude or the meridian altitude of a star of known
Three Mariner's Astrolabes in the Museum of the Forte da Ponta da Bandeira; Lagos, Portugal
Mariner's astrolabe from circa 1600.
Mariner's astrolabe made in 1645 by Nicolao Ruffo at The Mariners' Museum
Sodré astrolabe, the oldest mariner's astrolabe in National Museum of Oman, Muscat
Alidade
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An alidade or a turning board 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 triangulate a scale map on site using
Mariner's astrolabe
…or the meridian altitude of a star of known declination. Not an astrolabe proper, the mariner's astrolabe was rather a graduated circle with an alidade used to measure vertical angles. They were designed to allow for their use on boats in rough water or heavy winds, which astrolabes are ill-equipped…
A simple alidade for use with a ceiling projector
An example of an alidade on a circumferentor. Taken from the Table of Surveying, Cyclopaedia, Volume 2, 1728
Traverse plane-table alidade, c. 1898
A U.S. Navy sailor using a telescopic alidade