* Invented in ancient Greece, perfected by the Arabs and widely used by the Portuguese from early in the 15th century
* This device determined the latitude of a location
* It contained a pivoted disk representing half the heavens or the zodiac mounted within a frame which allows us to sight specific celestial objects
The magnetic compass
* Used for finding direction
* Improved design with gimbals in the 14th century
* Chinese innovation used for centuries for terrestrial uses only
* The introduction of the compass was a major breakthrough in navigation, as it allowed sailors to determine their course regardless of the weather conditions or the time of day.
The cross-staff
* Used to measure the altitude of celestial objects
* Made of two intersecting wooden staffs
* Used to ascertain the latitude when the altitude of a known celestial body (usually the Sun) is at its highest or lowest for the day