《周礼·冬官考工记·磬氏&车人》
如以躬的长度为一，上两个则为二，与躬合而为三，下两个长出于躬的部分是上两个所长出的一半。
上两个，与其身三；下两个，半之。
If the length of the gong is one, then the length of the upper two is two and combined with the gong, it becomes three. The part of the lower two that extends out of the gong is half the part of the upper two that extends out.