The sine quadrant, invented by Muhammad ibn Mūsā al-Khwārizmī in 9th century Baghdad, was used for astronomical calculations. Also known as the "Sinecal Quadrant" (the Arabic term for it is "Rubul Mujayyab"), it was used for solving trigonometric problems and taking astronomical observations. It was developed by al-Khwarizmi in the 9th century and remained prevalent until the 19th century. Its defining feature is a graph paper like grid on one side that is divided into sixty equal intervals on each axis and is also bounded by a 90 degree graduated arc. A cord was attached to the apex of the quadrant with a bead at the end of it to act as a plumb bob. They were also sometimes drawn on the back of astrolabes.