The Astronomical Quintant, also known as the Astronomical Goniometer, is an ancient astronomical instrument used to measure the elevation angle of celestial bodies. It consists of a quarter arc and a movable cursor. The principle of the astronomical pentameter is based on the method of triangulation. When the observer raises the astronomical pentameter towards the sky, the cursor can move to align with the line of sight of a celestial body. Surveyors can determine the elevation angle of celestial bodies by reading the scale on the cursor. Usually, the scale on an astronomical pentameter is spaced at intervals of five degrees, hence it is called a pentameter.