《宋书·志·卷十二》
为此我前一段时间制订法则，推算考求天文规律，考查了以前的典籍，用日食、朔日进行了验证，完备而精确地制定了精密的历法，就做到了对古今天象的推算与实际相比不早也不迟。
是以臣前以制典余日，推考天路，稽之前典，验之食朔，详而精之，更建密历，则不先不后，古今中天。
For this reason, some time ago, I formulated laws and regulations, deduced and studied astronomical laws, examined previous classics, and verified them with solar eclipses and first days of the month. I have formulated a precise and precise calendar perfectly and accurately, so that the calculations of ancient and modern celestial phenomena are compared with the actual situation. Not early or late.