TT #778 · Parashas Ki Seitzei · Seventh Aliyah · Passuk 25:15
A complete and just weight you shall have, a complete and just measure you shall have, that your days may be prolonged in the land that the Eternal your God is giving you.
Torah Temimah points to Bava Batra 89a.
TT lemma: אֵיפָה שְׁלֵמָה וָצֶדֶק.
תָּנוּ רַבָּנַן: מִנַּיִן שֶׁאֵין מוֹחֲקִין בִּמְקוֹם שֶׁגּוֹדְשִׁין וְאֵין גּוֹדְשִׁין בִּמְקוֹם שֶׁמּוֹחֲקִין? תַּלְמוּד לוֹמַר אֵיפָה שְׁלֵמָה.
English: Our Rabbis taught: From where do we know that one may not level off in a place where the custom is to heap, and may not heap in a place where the custom is to level off? Scripture says “a complete ephah.”
On the daf / in context: Local custom determines whether measures are heaped or leveled; deviation for fraudulent advantage is forbidden.
Derash requiring conformity to local measuring custom.
One must follow the local custom of heaping or leveling; one may not switch methods to one’s own advantage.