Halakhah su Deuteronomio 25:13

That He prohibited us from having weights and measures that are deficient, with us in our homes - even though one does not buy and sell with them. And that is His, may He be exalted, saying, "You are not to have for yourself in your pouch varying weight-stones, large and small" (Deuteronomy 25:13); and likewise, "varying ephah measurements" (Deuteronomy 25:14). And the language of the Gemara, Batra (Bava Batra 89b), is, "It is prohibited for a person to keep in his house a measure that is deficient or inflated, even if [he only uses it as] a chamber pot for urine." And you should not think that His saying, "You are not to have for yourself [...] "varying ephah measurements"; and "You are not to have for yourself [...] varying weight-stones" - [signifies] that they are two [distinct] negative commandments. Indeed, it is coming to round out the laws of the commandment, so that the types of measures are explained - and they are weight and measurement. It is as if He would say, "You should not have two measures with you - not for measuring, and not for weighing," as we explained in the Positive Commandments (Sefer HaMitzvot, Positive Commandments 208). And His saying, "You are not to have for yourself [...] varying weight-stones"; and "You are not to have for yourself [...] varying ephah measurements" - is like His saying, "You shall not charge interest to your brother; interest of money, interest of food, interest of anything upon which interest can be charged" (Deuteronomy 23:20) - which is one negative commandment that includes many types, all of which have the very same content. And it is not from the repetition of language that there is an expansion of commandments, as we discussed earlier in Principle 9. And something like this negative commandment already came before us; and that is His saying, ""no chametz may be seen [...], and no leaven may be seen" (Exodus 13:7). (See Parashat Ki Tetzei; Mishneh Torah, Theft 7.)

To not hold over deficient weights and measures: That we have been prevented, that we not hold over the deficient weights and scales in our homes - and even if we don't take and give (measure) with them in our purchases and in our sales, lest it be a snare. And about this is it stated (Deuteronomy 25:13), "You shall not have in your pouch alternate weights, larger and smaller." And so [too] (Deuteronomy 25:14), "You shall not have in your house alternate measures." And so did they, may their memory be blessed, say in Bava Batra 89b, "It is forbidden for a person to hold over a deficient or oversized weight in the midst of his home, and even if it is [used as a] bedpan for urine."