《明史·志·卷九》
将泛立积差六十六秒五十微作为被除数，用每段的日敷作为除数舆之相除二次，得二十七微，就是立差。
置凡立积差六十六秒五十微为实，以段日为法，除二次，得二十七微，为立差。
Use the ephemeris apparent difference of sixty-six seconds, fifty microseconds as the dividend, and use the daily increment of each section as the divisor to perform division twice, to obtain twenty-seven microseconds, which is the apparent difference.