《明史·志·卷十一》
将某交的定限度，舆初末限相减相乘，得敷除以千就是度，在正交、中交是加差，在半交是减差。
置某交定限度，与初末限相减、相乘，所得，千约之为度，在正交、中交为加差，在半交为减差。
Subtract the fixed limit degrees of a certain intersection from the initial and final limits, multiply the difference by the fixed limit, and division by one thousand to get the degree, which is added in the case of the perpendicular intersection and the mid-intersection and subtracted in the case of the half-intersection.