Restoration and re-creation in the Eastern Han
We look first at the situation in the early years of the restored Han dynasty. Liu Xin’s system continued in use for more than half a century. Then, in 85 CE, Liu Xin’s system was replaced. We have records of the practical and theoretical grounds on which the old system was rejected, and of the creation and implementation of a new system. Next we follow the story of how c. 92 CE Jia Kui advocated a fundamental innovation in both theory and practice: he insisted on the ecliptic as being central to astronomical observation and calculation. The richness of records from this period makes it easy to tell a detailed story of technical innovation in its fullest context, leading up to the work of Zhang Heng (78–139 CE), for whom astronomical calculation was just one of several fields in which he gained a reputation for exceptional originality.