《元史·本纪·卷十》
太史令王恂等上奏说： 在大都建立司天台，仪象圭表都用铜制成，应当增建一个高四十尺的铜制华表，这样影像才长而逼真。
太史令王恂等言： 建司天台于大都，仪象圭表皆铜为之，宜增铜表高至四十尺，则景长而真。
Wang Xun, the Imperial Historian, and others submitted a memorial saying: "Build an astronomical observatory in Dadu. All the astronomical instruments and sundials should be made of copper. A copper huabiao should also be built, with a height of 40 feet. This will make the image longer and more realistic.