Zu Chongzhi

Zu Chongzhi (429 to 500), courtesy name Wenyuan, was a Chinese astronomer, inventor, mathematician, politician and writer of the Liu Song and Southern Qi dynasties. He is most remembered for calculating pi as lying between 3.1415926 and 3.1415927, a precision that was not surpassed for nearly nine hundred years, and for the ratio 355/113, known in China as milu, which is the best rational approximation to pi among fractions with a denominator below 16600. He reached it by approximating the circle with a polygon of 24576 sides, using the algorithm of Liu Hui. With his son Zu Gengzhi he found the volume of a sphere as pi times the cube of the diameter over six by comparing it with a Steinmetz solid. His lost treatise Zhui Shu, written with his son, is thought to have treated cubic equations. He also compiled the Daming calendar, introduced in 465, and is credited with water powered trip hammer mills, paddle boats and a rebuilt south pointing chariot.