《北史·列传·卷七》
他又因河间人信都芳精于算术，把他招在客馆里，共同撰写了《古今乐事》、《九章》十二图。
又以河间人信都芳工算图。
He also heard that Fang Jing from Hejian was good at arithmetic. He invited him to his guest house and together they wrote "Ancient and Modern Music" and "Nine Chapters" with twelve illustrations.