Reprinted with permission from Ethics in the Market Place: A Jewish Perspective, published by The Library of Jewish Law, 2000, where extensive notes supplement the text presented here.
The Prohibition and its Source
In the [article, “Consumer Protection in Jewish Law: An Introduction,”] we cited the biblical sources for the prohibition against using defective weights and measures.
Defective weights and measures are discussed by [twelfth-century Spanish/North African philosopher and rabbi Moses ]Maimonides in his Laws of Theft:
“If one weighs with weights that are deficient by the standards agreed upon in his locality, or measures with a measuring vessel deficient by the agreed standards, he violates a negative commandment, for Scripture states (Leviticus 19:35), ‘You shall do no unrighteousness in judgment, in length, in weight, or in measure. (Maimonides, Mishneh Torah, Laws of Theft, 7:1)
“Similarly in measurement of land, if one deceives another when measuring land, he violates a negative commandment, for when Scripture says, ‘You shall do no unrighteousness in judgment, in length,’ ‘in length’ refers to land measurement.” (Maimonides, Mishneh Torah, Laws of Theft, 7:9)
Possession of Bad Weights and Measures
It is forbidden to keep a defective measuring device in one’s possession, even if it is not being used:
“Whoever keeps in his house or in his shop a false measure or weight violates a negative commandment, for Scripture states (Deuteronomy 25:13), ‘You shall not have in your bag diverse weights.’” (Maimonides, Mishneh Torah, Laws of Theft, 7:3)
For Clear and Standard Measures
Standard weights and measures are not to be prescribed unless gradations are readily apparent. Concerning this regulation, [Yehiel Michal Halevi Epstein, nineteenth-century author of] Arukh HaShulhan writes:
“The Sages established that measures should be so designed as to be recognizable at a glance, so there will be no mistakes and they will not be interchanged.” (Arukh HaShulhan, Hoshen Mishpat 231:4)
Maimonides codifies the penalty for false measure:
“The punishment for unjust measures is more severe than the punishment for immorality, for the latter is a sin against God only, the former against one’s fellow man. If one denies the binding character of the commandment relating to measures, he denies in effect the Exodus from Egypt which was the basis of the commandments; but if one acknowledges the commandment relating to measures, he thereby acknowledges the Exodus from Egypt, which rendered all the commandments possible” (Mishneh Torah, Laws of Theft 7:12).