《晋书·志·第八章》
杜预又认为周曲衰落，国家动荡不安，学者们没有得到当时真正施用的历法，现在传世的七种历法，都未必是各个王朝实际行用的历法。
杜预又以为周衰世乱，学者莫得其真，今之所传七历，皆未必是时王之术也。
Du Yu further claimed that when the Zhou dynasty waned and the country fell into disorder, scholars did not obtain the astrology that was actually used at the time; and of the seven types of astrology that are now passed down, not all of them were the astrology actually used by the various dynasties.