What official position did Zhang Heng hold in Shi Jing?

After Zhang Heng arrived in Beijing, he began to work as a doctor in Shangshutai Yamen, an official who drafted documents. Three years later, he was promoted to assistant minister of Shangshu, and then transferred to Taishiling the next year. Taishiling's duty is to take charge of the calendar, observe astronomy and meteorology and so on. The imperial court held sacrificial ceremonies, and Taishiling chose the so-called "auspicious day". Every sign that the feudal emperor thought was "auspicious" or any disaster was also recorded by Taishiling and reported to the emperor.