Chen Qingying, Professor of History and Director of the History Studies Institute under the China Tibetology Research Center in Beijing, writes that the Ming court conferred new official positions on ex-Yuan Tibetan leaders of the Phachu Kargyu and granted them lower-ranking positions. Of the county (zong or dzong) leaders of Neiwo Zong and Renbam Zong, Chen states that when "the Emperor learned the actual situation of the Phachu Kargyu, the Ming court then appointed the main Zong leaders to be senior officers of the Senior Command of Dbus and Gtsang." The official posts that the Ming court established in Tibet, such as senior and junior commanders, offices of Qianhu (in charge of 1,000 households), and offices of Wanhu (in charge of 10,000 households), were all hereditary positions according to Chen, but he asserts that "the succession of some important posts still had to be approved by the emperor," while old imperial mandates had to be returned to the Ming court for renewal.