You shall not have in your house different ‘ephah’ measures, a big one and a small one. A whole and honest weight-stone you shall have… (Devarim 24:14-15) These different measures were used to cheat in buying and selling. Not only are we forbidden to use tools of trickery, we are also banned from owning them. The Ben Ish Hai writes that owning tools of trickery is very severe because one who owns them is doing something wrong all the time, even during Neilah on Yom Kippur!