Positive commandment · Mitzvat Aseh #208 of 613
To balance scales with correct weights
לצדק מאזניים עם המשקלות
The verse · Vayikra 19:36
מֹאזְנֵי צֶדֶק אַבְנֵי־צֶדֶק אֵיפַת צֶדֶק וְהִין צֶדֶק יִהְיֶה לָכֶם אֲנִי ה׳ אֱלֹהֵיכֶם אֲשֶׁר־הוֹצֵאתִי אֶתְכֶם מֵאֶרֶץ מִצְרָיִם
“Just balances, just weights, a just efa, and a just hin, shall you have: I am the Lord your God, who brought you out of the land of Miżrayim.”
The Rambam’s words
To balance scales with correct weights, as [Leviticus 19:36] states: "You shall have correct scales, with correct weights."
לצדק מאזניים עם המשקלות, שנאמר: "מאזני צדק אבני צדק" (ויקרא יט, לו).
Why · Sefer HaChinuch #259
Having just scales, weights and measures
“The root of the commandment of righteousness and the distancing from robbery and deceit among people is well-known to all intelligent people.”
Who & when
“And [it] is practiced in every place and at all times by males and females.”
Where in the Mishneh Torah
Hilchot Theft הלכות גניבה