How to correctly calculate the value of pi is an important topic in the history of mathematics in the world. Mathematicians in ancient China attached great importance to this problem and began to study it very early. The ratio of the ancient diameter to one week and three weeks was put forward in Parallel Calculation of Weeks and Nine Chapters Arithmetic, and the pi was set at three, that is, the circumference of a circle was three times the diameter. Since then, after successive explorations by mathematicians of past dynasties, the calculated pi value has become more and more accurate. At the end of the Western Han Dynasty, in the process of designing and making a round bronze tiger (a measuring instrument) for Wang Mang, Liu Xin found that the ratio of one diameter to three circumference in ancient times was too rough. After further calculation, the value of pi is 3. 1547. The value of pi calculated by Zhang Heng, a famous scientist in the Eastern Han Dynasty, is 3. 162. During the Three Kingdoms period, the value of pi calculated by mathematician Wang Fan was 3. 155. Liu Hui, a famous mathematician in Wei and Jin Dynasties, created a new method to calculate pi when he annotated Nine Chapters Arithmetic. He set the radius of the circle as 1, divided the circle into six equal parts, made the inscribed regular hexagon of the circle, and calculated the circumference of the inscribed regular hexagon by pythagorean theorem. Then inscribed with dodecagon, icosahedron, etc. In turn, until the circle is inscribed with 192 polygons, its side length is 6.282048, and the more sides inscribed with regular polygons in the circle, the closer its side length is to the actual circumference of the circle, so the value of pi at this time is the side length divided by 2, and its approximate value is 3.14; It shows that this value is less than the actual value of π. Liu Hui realized the concept of limit in modern mathematics in secant. The tangent circle method he founded is a major breakthrough in the process of exploring the value of pi. In order to commemorate this achievement of Liu Hui, later generations called the value of pi he obtained "Hui rate" or "Hui technique".

Zu Chongzhi thinks that Liu Hui is a scholar who has made the greatest achievements in the study of pi during the hundreds of years from Qin and Han Dynasties to Wei and Jin Dynasties, but it has not reached an accurate level, so he makes further in-depth research in order to find a more accurate value. The research and calculation results prove that pi should be between 3. 14 15926 and 3. 14 15927. He became the first person in the world to calculate the exact value of pi to seven decimal places. It was not until a thousand years later that this record was broken by Arabian mathematician Al Cassie and French mathematician Viette. Zu Chongzhi's "secret rate" was not called "Antuoni's rate" by German until 1000 years later, and some people with ulterior motives said that Zu Chongzhi's pi was forged after western mathematics was introduced into China in the late Ming Dynasty. This is a deliberate fabrication. The ancient book that records Zu Chongzhi's research on pi is the history book of Sui Shu in Tang Dynasty, and the current Sui Shu was published in Bingwu Year (A.D. 1306). Like other modern versions, the record of Zu Chongzhi's pi happened more than 300 years before the end of Ming Dynasty. Moreover, many mathematicians before the Ming Dynasty quoted Zu Chongzhi's pi in their works, which proved Zu Chongzhi's outstanding achievements in the study of pi.