《汉书·志·律历志下》
不满一百三十五的，就十三得一月，满一百三十五，计算所得的，从正开始，计算除去的，就是食月。
不盈者，加二十三得一月，盈百三十五，数所得，起其正，算外，则食月也。
If it is less than one hundred and thirty-five, thirteen will get one month, one hundred and thirty-five, calculate the obtained value, start from the positive, and calculate the removed value, which is the eclipse month.