《明史·志·卷十一》
推算加减差：以相距度与转定积度相减的差作为被除数，用朔弦望相距日作为除数与之相除，得敷比相距度多的就是加差，少的就是减差。
推加减差以相距度与转定积度相减为实，以其朔弦望相距目为法除之，所得视相距度多为加差，少为减差。
Calculate the difference between addition and subtraction: take the difference between the average distance and the converted fixed degree as the dividend, and divide it by the number of days between the new moon, the first quarter, and the full moon as the divisor. To get the degree of distance, if the average distance is more than converted fixed degree, it is the difference between addition and subtraction, and if it is less, it is the difference between subtraction and addition.