《汉书·志·律历志上》
它的意义包括了天地所有的变化，用天地五位的最后一个数十来乘以六十四，得六百四十分，应了六十四卦，这是太蔟的积数。
其义极天地之变，以天地五位之合终于十者乘之，为六百四十分，以应六十四卦，大族之实也。
Its meaning includes all the changes of Heaven and Earth, and multiplied by sixty-four, the last tens of the five positions of Heaven and Earth, makes six hundred and forty, which is the sixty-four hexagrams, and this is the accumulation of Tai Cu.