Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 208
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 208, with English translation by Maimonides (Rambam).
לצדק מאזניים עם המשקלות, שנאמר: "מאזני צדק אבני צדק" (ויקרא יט, לו).
To balance scales with correct weights, as [Leviticus 19:36] states: "You shall have correct scales, with correct weights."