He was not the first Chinese astronomer to discover the precession of the equinoxes (Yu Xi did so in the fourth century) but he was the first to take this into account in calendar calculations.
Siya ay hindi ang unang Chinese astronomer upang matuklasan ang pangunguna ng equinoxes (Yu XI did kaya sa ika-apat na siglo) ngunit siya ang unang na tumagal ito sa account sa kalendaryo kalkulasyon.