suansheng: Liu Hong (about 13-196), born in Mengyin (now Mengyin County, Shandong Province) of Taishan County in the Eastern Han Dynasty, was born in the 4th year of Yongjian in the Eastern Han Dynasty (AD 129) and died in the 15th year of Jian 'an (AD 21). He was an outstanding astronomer and mathematician in ancient China. During Yan Xi's reign of Emperor Huan of Han Dynasty (158-166), Liu Hong said, "Take a captain as an official, and pay homage to Liang Zhong". Being an official for several years, he is honest and upright, and officials and people are afraid and respectful. Liu Hong has been studious and knowledgeable since childhood. As he was a royal clan of Lu, he became a court minister when he was young, which was endowed with unique conditions for displaying his political ambitions and devoting himself to studying astronomical calendars. Liu Hong's talent was valued by the imperial court. "The Book of the Later Han Dynasty" said that Hong Shan counted that there was no spouse in the world. Therefore, during the reign of Emperor Guanghe of Han Ling, he was recommended by Taishi Cai Yong and transferred back to the capital, specializing in calendar research. During this period, he not only participated in "testing the sun and the moon" according to the emperor's will, but also reviewed and collated the research results submitted by others, and also compiled the research results for many years into monographs such as Dry Elephant Calendar, Seven Obsidian Techniques and Nine Arithmetic Chapters. After careful study, he found that the Quarter Calendar adopted at that time was inaccurate, so he calculated and improved it with reference to the calendars of previous dynasties, and created the first calendar in China, the Dry Elephant Calendar. "Dry Calendar" is a calendar that considers the uneven movement of the moon. When calculating solar eclipses and eclipses, the method of determining the new moon is adopted. It is measured that the length of the near moon point is 27.558 days, and the angle between the ecliptic and the white road is about 6 degrees. From this, the difference between the actual daily movement degree and the average movement degree can be found out, so that the period can be calculated by the flat moon. Ganxiang Calendar had a great influence on the revision of calendars in past dynasties, and it was used by later generations. Another important achievement of Liu Hong was to supplement the Book of Laws and Calendars of Han Dynasty with Cai Yong, many of which were adopted by the later Book of Laws and Calendars of Han Dynasty. Abacus calculation is a tool for calculating with an abacus. The invention of abacus has made a leap in people's computing ability. The term "abacus" was first seen in the book "Notes on Numerology" written by wei ren Xu Yue in the Eastern Han Dynasty. Xu Yue said in the book: "Liu Huiji is knowledgeable and biased towards mathematics ... There are still many kinds of Li Shouzhu techniques, one of which counts." Liu Huiji mentioned by Xu Yue is Liu Hong. Some people say that Mengyin is the hometown of abacus, and Liu Hong is the father of abacus, and is honored as "the sage of abacus". Abacus is one of China's five great inventions.