《梦溪笔谈·象数一》
不过大凡立冬的晷影与立春的晷影是差不多的，如今旧历所用的这两种晷影长短不同，可知旧历冬至节气的确定有偏差；大致移动五十余刻，立冬、立春的晷影长度才能均匀。
凡立冬晷景，与立春之景相若者也。今二景短长不同，则知天正之气偏也。移五十余刻，立冬、立春之景方停。
However, the length of the shadow at the beginning of winter and the length of the shadow at the beginning of spring are nearly the same; now the length of these two kinds of shadow in the old calendar are different, so the determination of the winter solstice solar term of the old calendar is wrong; it is roughly moved for more than fifty moments, the length of the shadow at the beginning of winter and the beginning of spring can be even.