《宋书·志·卷十二》
推算发生合月份的朔日：将入纪月乘以通数，再除以曰法，其商为积曰，余数为小余。
推合月朔：以通数乘入纪月，满日法得一为积日，不尽为小余。
Calculate the first day of the month when the conjunction happens: Multiply the chronological month by the common number, then divide it by the day method, the quotient is the cumulative day, and the remainder is the minor remainder.