What is the Dayan calendar?

Great Yan Li was written by one monk and one party (683-727) in the 15th year of Emperor Xuanzong of the Tang Dynasty, and was later compiled by Chen (667-730). Published in the seventeenth year of Emperor Xuanzong of the Tang Dynasty (AD 729), it was used in the tenth year of Tianbao (AD 75 1 year). In the 21st year of Kaiyuan (AD 733), it was introduced to Japan and used in Japan for nearly a hundred years. Da Yan Li is well-structured and well-organized. * * * There are seven calendars, and the specific calculation method is described. In addition, there are 12 calendar discussions (including three short examples) to talk about the theoretical problems of calendars. It was a paper written by Da Yanli, commonly known as Da Yanli Discussion. The formulation of the Great Yan Li started with the manufacture of instruments, and the basic astronomical data were determined through actual observation, which is a scientific method. After the establishment of the Dayan calendar, we have a correct and comprehensive understanding of the uneven motion of the sun and the moon. Through practical observation, the fallacy of "one inch difference, 108 thousand miles" has been broken for thousands of years. In the calculation method, the unequal interval quadratic difference interpolation method in Dayan Calendar is improved compared with that in Huangji Calendar.