《史记·八书·礼书》
因为，绳墨是直的标准；秤锤是轻重的标准；圆规和角尺是方圆的标准；礼则是为人处事的最高标准。
故绳者，直之至也；衡者，平之至也；规矩者，方员之至也；礼者，人道之极也。
For, this marking line and square are the standard by which crookedness is tested; this steel-yard is the standard by which heaviness is tested; the compass and square are the standards by which roundness is tested; and the propriety is the standard by which humanity is tested.