《北史·列传·卷七十七》
实在由于太阳运行慢，那么月亮容易赶上太阳，让日月相会早加时；太阳运行快，那么月亮追赶太阳稍慢，让日月相会晚加时。
实由日行迟，则月逐日易及，令合朔加时早；日行速，则月逐日少迟，令合朔加时晚。
Since the sun is displaced for slow, it was easy for the moon to catch up with it and thus happen early than scheduled. If the sun is displaced for fast, it was a little slower for the moon to chase after it, and thus the moon's arrival became late. 