《明史·志·卷十三》
求东西定差：将合朔时的东西差化为秒，再将比数分化为秒与之相乘得到纤数。按六十进制为微、秒、分，再加合朔时的东西差，只有加，没有诚。就是定差。
求东西定差置合朔时东西差通秒，以比敷分通秒乘之为纤以六十收之为微、为秒、为分，以加合朔东西差，为定差。
Find the fixed east-west difference: Convert the east-west difference at the time of the conjunction into seconds, then convert the ratio into seconds and multiply by it to get the number of fibers. According to the sexagesimal system, it is microseconds, seconds, and minutes, then add the east-west difference at the time of the conjunction, only add, no sincerity. That's the fixed difference.