- An old instrument used for measuring the altitude angle of celestial body. It can measure angles up to 90°.
- The curved yoke of a 90° arc that controls the rudder as a tiller (AKA steering quadrant).
17th century for the instrument. Mid-19th century for the steering device. From Latin, quadrans, meaning one quarter.
There are many different types of quadrants which can be used to take celestial readings and give the observer various kinds of information.
Rogers, J.G. (1985). Origins of Sea Terms. Mystic Seaport Museum.