《明史·志·卷七》
只是天实际上是圆体，与平行不同，旧历用的三差法，都是从勾股平行来确定的，和天体不合。
第天实圆体，与平行异类，旧所用三差法，俱从句股平行定者，于天体未合。
It's just that the sky is actually a circle, different from parallel. The three-difference method used in the old calendars is determined from right-angle triangles, which is not in line with celestial bodies.