get / take / have the measure of sb
摸清某人的底细
to form an opinion about sb's character or abilities so that you can deal with them
After only one game, the chess champion had the measure of his young opponent.仅仅一局过后,这位国际象棋冠军就摸清了年轻对手的实力。
释义来自《牛津高阶英汉双解词典》第 9 版