《北史·列传·卷七十七》
张胄玄制定的历法，和古代历法不同的地方有三处：其一，宋人祖冲之在每年结束的最后，使用差分，冬至逐渐变化，不沿原来的轨道，每过四十六年，相差一度。
胄玄所谓历法，与古不同者三事：其一，宋祖冲之于岁周之末，创设差分，冬至渐移，不循旧轨，每四十六年，却差一度。
There were three places where Zhang Zouxuan's formulated calendar was different from the ancient calendar: first, at the end of each year, the Song Dynasty and Zu Chongzhi used differentials, and the winter solstice gradually changed, not along its original orbit. Every 46 years, there was a difference of one degree.