A quadrant is an instrument that is used to measure angles up to 90簞. It was originally proposed by Ptolemy as a better kind of astrolabe. Several different variations of the instrument were later produced by medieval Muslim astronomers.

Beijing's Ancient Observatory was built in 1442 during the Ming Dynasty and is one of the world's oldest. It served the Ming and Qing astronomers in their star-gazing reports for the Emperor. As he was considered the Son of Heaven, the movements of the heavenly bodies were an important affair. Another function was to assist sea navigation, with Muslim scholars recruited for their expertise in the area.