An instrument for measuring altitudes, variously constructed and mounted for different specific uses in astronomy, surveying, gunnery, etc., consisting commonly of a graduated arc of 90°, with an index or vernier, and either plain or telescopic sights, and usually having a plumb line or spirit level for fixing the vertical or horizontal direction.

Early instrument used to measure angles and altitudes in astronomy and navigation.

a measuring instrument for measuring altitude of heavenly bodies

a device for measuring angles used by the Greeks, Muslims and early Europeans for astronomy/astrology and navigation

A simple astronomical tool that measures star altitudes and can be used to measure latitude, the distance moved north or south.

The quadrant is an instrument used to measure altitude.

An instrument once used by astronomers and sailors to measure the angle of the stars and planets in the sky. They could use this information to find their location on the earth.