If you use someone or something as a yardstick, you use them as a standard for comparison when you are judging other people or things.
例句
There has been no yardstick by which potential students can assess individual schools before signing up for a course.有意就读的学生在报名参加一门课程前没有任何参照标准去衡量各个学校的水平。She had never had a real boyfriend before and so had no yardstick by which to compare Charles's behaviour...她以前从没有过真正的男朋友，所以没有可参照的标准来对比查尔斯的行为。