Ulugh Beg’s zīj, an astronomical handbook with tables and new star catalogue in Persian was the result of innovative observational and calculational methods developed by Ulugh Beg and his colleagues (who included Ghiyāth al‐Dīn Jamshīd al-Kāshī, Qāḍīzāde al‐Rūmī, and ʿAlī al-Qūshjī) at the Samarqand observatory to rectify errors found in the Zīj-i Īlkhānī, which was produced at the Maragha observatory under the directorship of Naṣīr al-Dīn al-Ṭūsī (d. 672/1274).