《史记·七十列传·张丞相列传》
但是后来黄龙果然出现在天水郡的成纪县于是文帝就把公孙臣召到了朝廷，并任命他为博士，让他负责草拟顺应土德的历法制度。同时，改定元年。
其後黄龙见成纪，於是文帝召公孙臣以为博士，草土德之历制度，更元年。
But later a yellow dragon appeared in Chengji County of Tianshui County. So Emperor Wen called Gongsun Chen to the court and appointed him as a doctor to draft the calendar system that would follow the virtue of soil. At the same time, the first year was changed.