《明史·志·卷十三》
将正午时月亮超过太阳的度数，计算方法见后面月食时月亮每一时刻超过太阳的度数。化为秒，乘以二十四作为被除数，将月亮的日行度数，减去太阳的日行度数，化为秒作为除数，二者相除即是时数时以下的零数乘以六十化为分，分以下的零数乘以六十化为秒，三十秒以上收为一分，六十分收为一时，加起来就是食甚的时间。
置午正太阴行过太阳度，通秒，以二十四乘之为实，置太阴日行度，减太阳日行度，通秒为法，除之为时。时下零数以六下通之为分，分下零数以六十通之为秒，三十秒已上收为一分，六十分收为一时，共为食甚凡时。
Convert the degree to which the moon surpasses the sun at noon into seconds. Divide this number by 24 to get the denominator. Convert the moon's daily movement and the sun's daily movement into seconds and divide the denominator by these numbers. Multiply the number below the decimal point by 60 to get the minutes and then do the same to get the seconds. If the number of seconds is greater than 30, convert it to minutes and if the number of minutes is greater than 60, convert it to hours. Add these numbers together to get the time of the maximum obscuration.