We'll elaborate on what we said in the last Mishnah regarding the halachot (laws) of weights and measures. What did we say in the last Mishnah? We said that when it comes to weights and measures, a person is obligated to clean them to make sure there are no substances that would weigh down the weights and cheat customers. But that was only talking about lach (things that are moist). That was only talking about when the weights are being used for things that are moist, like meat, fish, oily things, and things that contain liquid, which would stick to the weights. Therefore, to remove the oils, you have to clean them regularly. But if you're dealing with something yavesh (dry), like grain or spices, or things of that nature, there's no need to wipe them down. Nothing sticks to the scale. Unless somebody actually sees something that needs to be wiped down, some actual dirt, there's no need to do it periodically or on certain dates.
In addition to making sure that a person's scales are clean, the Torah obligates him to provide a little extra merchandise to the people buying from him. There are different ways to do this. A person could add more to the scale during the weighing, or just give a fixed percentage of goods at the end of the sale. The Mishnah will talk about both methods that were used. The custom was to add extra goods to the scale at the point of sale, and the seller has to add enough for the scale to tilt in the buyer's favor by a tefach (handbreadth). He has to add enough merchandise to the scale so that the side with the items is lower than the side with the actual weight. You have to think about how they used weights and measures in those days. They'd have one side of the scale with a certain weight, and the other side would have the merchandise. All things being equal, if they were at the same height, that means you had, measure for measure, exactly what you were looking for. So what we're saying is that the side with the merchandise has to be not equal; it has to be at least a tefach lower, to include the extra merchandise a seller is obligated to throw in for the buyer.
But if the custom in the place was to weigh the items with everything even, the weights on one side and the merchandise on the other, and to add only an extra percentage of the sale at the end, he would give the buyer the extra weight using the following formula. He'd give him one-tenth of a measure for every ten measures of liquid that he sells. Basically, he would give him one percent extra on the sale when it comes to liquids. And he would give him one-twentieth of a measure for every twenty measures of dry goods. That's one quarter of one percent, which equals one-four-hundredth of the sale when talking about dry goods.
The custom also had to be followed when it came to what type of containers were being used for selling. If the custom was to use a small container, and even when selling a large amount you'd have to keep scooping with that small container, you're not allowed to use a large container instead. And the opposite: If the custom was to use a large container, you're not allowed to use a small container. You have to use exactly what was used according to that custom, and that would affect the extra amounts someone was adding to the weights, which you're obligated to add for each buyer. If you were measuring smaller amounts at a time, then you'd have to make the scales adjust by a tefach continuously, and therefore you'd keep providing him with more. That's why it would be applicable to that halacha (Jewish law).
The final ruling of the Mishnah is: How much do you have to fill containers that were being used to sell dry goods, like flour or spices? In a place where the custom was to level off the container until it was even with the top, after you filled it all the way, you don't heap more goods on top of that level. But if the custom was to put goods on top of the container, at the brim of the container, you're not allowed to level it off, even if you're charging less for the leveled container. You have to follow the local custom of what was done. People had certain ways of wanting things and expressing their wants, and it would go by local custom, so you have to follow that local custom when filling up customers' containers.