Core Viewpoint - The article discusses the historical significance of the "Shou Shi Li" (授时历) and the innovations in astronomical instruments during the Yuan Dynasty, highlighting the transition from traditional observational methods to mathematical modeling in ancient Chinese astronomy [1][2]. Group 1: Historical Context - The exploration of time by humans evolved from simple observations of natural phenomena to the need for precise calendars as agricultural civilization developed [1]. - The "Si Hai Ce Yan" (四海测验) conducted by scholars like Xu Heng, Wang Xun, and Guo Shoujing involved extensive astronomical measurements across 27 locations, laying the foundation for the new calendar [1]. Group 2: Innovations in Astronomy - Guo Shoujing reformed traditional astronomical instruments, creating the "Jian Yi" (简仪) and "Yang Yi" (仰仪), which significantly improved observational accuracy and efficiency, surpassing the precision of the Song Dynasty's instruments [2]. - The "Jian Yi" became the precursor to modern equatorial instruments, symbolizing the ancient concept of "Heavenly Round and Earthly Square" through its design [2]. Group 3: The "Shou Shi Li" - The "Shou Shi Li" was developed based on precise astronomical measurements, achieving a year value of 365.2425 days, matching the Gregorian calendar and being 300 years ahead in precision [2]. - The calendar's solar terms were calculated with remarkable accuracy, differing by only 2 minutes from modern astronomical results, and it was used for over 380 years, influencing agricultural practices in China and neighboring regions [2].