Calling something a " yardstick" is to say it is a standard by which to judge something: The teachers used the test results as a yardstick for how much their students learned this year.
There are no yard measures, neatly divided into the fractions of an inch, that one can lay against the qualities of a good mother or the devotion of a daughter, or the fidelity of a sister, or the capacity of a housekeeper.