This instrument is a reproduction of the Nautical Astrolabe called of “Valence” for the Irish island it was found, and belonged to the Armee of Philipe II (16th century). It´s placed in the National Maritime Museum of Greenwich and the replica used is in the Naval Museum of Madrid. The nautical astrolabe is a simplification of the planispherical or astronomical astrolabe and its fundamental purpose is to obtain one the latitude, by observing the altitude of the sun or other stars as the Pole Star.