, along with 2 quadratic equations and 2 double quadratic equations.
It was known that the Chinese calendar at that time was in need of reform since, although only in operation for a few years, already predictions of eclipses were getting out of step. In 623, together with Zu Xiaosun, a Civil Servant, he was assigned to report on problems with the calendar—although only recently adopted, it was already out of step with the eclipses. In fact Wang did not approach this in a sophisticated way; he proposed to ignore the irregularity of the sun's motion and also the precession of the equinoxes—both had already been incorporated in calendar calculations by Zu Chongzhi in the fifth century.
