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.有意就讀的學生在報名參加一門課程前沒有任何參照標準去衡量各個學校的水平。She had never had a real boyfriend before and so had no yardstick by which to compare Charles's behaviour...她以前從沒有過真正的男朋友，所以沒有可參照的標準來對比查爾斯的行為。