The book "Shixian Calendar" was formulated in the late Ming Dynasty and officially adopted Dingqi. This is the fifth and last major reform in Chinese history. At the end of the Ming Dynasty, after more than 40 years of actual testing, Western calculations were quoted and compiled into the "Chongzhen Almanac", which was declared dead before it was officially promulgated. In the early Qing Dynasty, Catholic Jesuit missionary Tang Ruowang deleted and compressed it and submitted it to the Qing government. The Qing government renamed it the "New Western Calendar" and compiled an almanac based on its data, called the Shixian Calendar. The Shixian calendar was abolished and the whole year was divided into 24 parts, based on which the flat qi (constant qi) of the solar terms was determined, and the fixed qi based on the position of the sun on the ecliptic was officially adopted. The old calendar used in modern times is the Shixian calendar, usually called the Xia calendar or the lunar calendar.