《周礼·冬官考工记·磬氏&车人》
把弗矢的长度分为七等分，三等分在前，四等分在后，则前后重量相等。
杀矢，七分三在前，四在后。
Divide the length of the featherless arrow into seven equal parts, with three parts in front and four parts at the back, so that the weight distribution was equal.