Decimals are produced and developed in the need of actual measurement and integer operations (such as division and root). With the development of society, the requirement of measurement accuracy is gradually improved, which is reflected in mathematics, that is, the requirement of quantity representation accuracy is improved. At first, human beings can only use integers to represent quantities, and then add words such as "surplus", "odd" or "strong" and "weak" at the end of the represented quantities. When numbers are needed to express this difference more accurately, two representations are gradually formed: one is to express the rest of the integer with fractions; The other is to develop the system of weights and measures, and use smaller units of weights and measures to express related quantities. In ancient China, the decimal unit system was formed earlier. When Liu Hui annotated Nine Chapters Arithmetic, the units of length were: feet, feet, inches, minutes, millimeters, seconds, and suddenly, which was the smallest unit. In the calculation, he takes sudden as the unit, as follows. Liu Hui is the earliest mathematician who used decimals in Chinese history. It's a pity that he didn't improve the counting method slightly and pushed the decimal to the modern level. Instead, decimals are used as general fractions.