Zhang Fei's handwriting is still preserved until now!
Guan Yu was not the inventor of the abacus.
The inventor of the abacus is Xu Yue (? ~ 22) The word Gonghe. A famous mathematician and astronomer in the Eastern Han Dynasty, the world's first "abacus" proposer and "abacus" recorder. Donglai (now Laizhou City) people. During the reign of Emperor Lingdi in the Eastern Han Dynasty, Liu Hong, a famous astronomer, created a "dry elephant calendar" and "personally taught it" to Xu Yue. Xu Yueqian studied the calendar such as dark, new moon, string, moon and moon eclipses, and further improved the "dry calendar", and later taught the calendar to Kan Ze, the secretary of the State of Wu, so that the calendar could be implemented in the State of Wu. The study of calendar laid a solid foundation for Xu Yue to engage in arithmetic research in the future. He collected a large number of mathematical data since the pre-Qin period, and wrote many mathematical works, such as "Notes on Mathematical Techniques" and "Calculation of Classics". "Notes on Numerology" recorded the essence of his arithmetic question and answer with Liu Hong in detail, and introduced 14 calculation methods. The style of abacus was recorded for the first time, and it was named "abacus calculation" for the first time. Emperor Xiandi Yankang died in the first year (22).