《百战奇略·第八卷·气战》
因此，作战中必须度量敌人进至距我六七十步以内，才可以击鼓，命令士兵奋勇进战。
须度敌人之至六七十步之内，乃可以鼓，令士卒进战。
Therefore, during combat, it is necessary to gauge when the enemy is sixty to seventy paces away before you can beat the drum and order the soldiers to fight bravely.