《宋史·志·卷一》
首先约制确定四方，因为三个表南北相互重合，使底座与表贴近，表分别相距二尺，使它们各自树立正直。
先约定四方，以三表南北相重，令趺相切，表别相去二尺，各使端直。
First, it is determined that the four sides are in approximate alignment, because the three tables overlap from the south and north, so that the bases are close to the tables, and the tables are two feet apart each, so that they stand upright.