The word "standard," meaning "level of quality" or "rule" evolved from the physical battle flag on a pole, as in "standard bearer." So for things like standardized lengths of measurement, you could say "we follow the king's standard for what a foot is," which was a metaphor for following the king's rule on what that length was. That further stretched into a level of quality or conduct that needed to be achieved.

This might be obvious to some, but I only recently realized. A standard was originally a flag on a poll, meant to be visible across a battlefield as a direction for all to follow.