Biaodushuo 表度說

Biaodushuo 表度說 "On the tabulation of degrees" is a text on astronomy compiled during the late Ming period 明 (1368-1644) by the Italian Jesuit Sabatino de Ursis (1575-1620; Chinese name Xiong Sanba 熊三拔) and Zhou Ziyu 周子愚. De Ursis arrived in China in 1606 and studied Chinese under Matteo Ricci (1552-1610; Li Madou 利瑪竇), becoming one of Ricci's key assistants. He later collaborated with Xu Guangqi 徐光啟 (1562-1633) and Li Zhizao 李之藻 (1571-1630) to translate Western texts on astronomy. He participated in measuring the longitude of Beijing, as well as designing various water-drawing and storage devices. In 1616, he was expelled from China and later passed away in Macau. He also authored the Taixi shuifa 太西水法 "Hydraulic methods of the Far West" and Jianpingyi shuo 簡平儀說, an explanation of the levelling instrument, among other works.

The Biaodushuo examines gnomonic measurements, tracing their origins to the tugui 土圭, an ancient Chinese sundial-like instrument. De Ursis introduced a more efficient method that allowed for flexible positioning of the gnomon to ascertain seasonal timings. The book is divided into five sections, each detailing his methods and accompanied by illustrative diagrams. The most notable contributions are the discussions on "The earth as a spherical body" (Di ben yuan ti 地本圓體) and "The earth is smaller than the sun" (Di xiao yu rilun 地小於日輪), which served as an introduction to Western natural science in China.

It was printed in the Ming period and is included in the series Tianxue chuhan 天學初函 and Siku quanshu 四庫全書.