Page "Zhang Heng" Paragraph 4

In 112, Zhang was summoned to the court of Emperor An of Han ( r. 106 – 125 ), who had heard of Zhang's expertise in mathematics.

When he was nominated to serve at the capital, Zhang was escorted by carriage — a symbol of his official status — to Luoyang, where he became a court gentleman working for the Imperial Secretariat.

He was promoted to Chief Astronomer for the Han court under Emperor An, serving his first term from 115 – 120 and his second under the succeeding emperor from 126 – 132.

As Chief Astronomer, Zhang was a subordinate of the Minister of Ceremonies, the latter one of Nine Ministers ranked just below the Three Excellencies.

In addition to recording heavenly observations and portents, preparing the calendar, and reporting which days were auspicious or not, Zhang was also in charge of an advanced literacy test for all candidates of the Imperial Secretariat and Censorate ( who were expected to know at least 9, 000 Chinese characters and all major writing styles ).

Under Emperor An, Zhang also served as Prefect of the Majors for Official Carriages under the Ministry of Guards, in charge of the reception of memorials ( containing policy and administrative suggestions ) submitted to the throne as well as nominees for official appointments.