The Beraisa prohibits compressing the contents of the measure when it is customary to heap them, or vice-versa - even with the consent of the purchaser or the seller (respectively).

We learn this from the Pasuk in Ki Seitzei "Eifah Sheleimah (va'Tzedek) Yih'yeh lach". From the word "va'Tzedek", we learn - that this is forbidden even if the seller deducts from the price, or the purchaser adds to the price, to compensate any loss caused by the change.

Were the seller permitted to compress the measure provided he deducted from the price - he would need to deduct a third, because the Shi'ur of Gedishah is a third of the regular volume.

Following exactly the same pattern, we learn from the continuation of the Pasuk ...

... "Even Sheleimah (va'Tzedek) Yih'yeh lach" - that, after weighing, one may not add goods on to the scale, in a town where the Minhag is to tip the scales during the course of the weighing, or vice-versa.

... " ... va'Tzedek" - that this is forbidden even with the consent of the other party.

Rav Yehudah mi'Sura learns from the Pasuk "Lo Yih'yeh l'cha ...

... be'Veischa ... Eifah va'Eifah, Gedolah u'Ketanah" - that someone who uses false measures will ultimately end up with nothing in his house.

... be'Kischa" ... Even va'Aven, Gedolah u'Ketanah" - that someone who uses false weights will end up with an empty purse.

The Beraisa Darshens from the Pasuk "Even Sheleimah va'Tzedek Yih'yeh lach" - that Beis-Din are obligated to appoint inspectors to check the weights and measures of the town, and to punish the transgressors.

The Tana does not consider this necessary when it comes to price control, in order to penalize those who raise their prices - because those who do will simply find their customers buying elsewhere.

Nevertheless, the B'nei Nesi'ah - used to send their inspectors round to check on them as well.

A 'horn of flesh' grew on Karna's eye - because, when Shmuel instructed him to announce the previous distinction between Midos and She'arim, he announced instead that Beis-Din must appoint inspectors for both. So Shmuel cursed him that this should happen.

Shmuel chose specifically that punishment - because it was a play on his name 'Karna'.

Karna, on the other hand, based his ruling on Rami bar Chama Amar Rebbi Yitzchak, who ruled that way because of the swindlers (see Rabeinu Gershom)

When the Tana rules that one fulfills the request of the purchaser to sell a Litra, half a Litra or quarter of a Litra, he means either that this is the minimum size weights that Chazal instituted (and that if a purchaser wants to buy less than that, the seller should use coins) or - that they fixed the weights and measures using these denominations as opposed to a third and a fifth of a Litra (see Rabeinu Gershom).

One weighs three-quarters of a Litra - by placing a Litra weight on the scales and a piece of meat weighing a quarter of a Litra on the other side to offset the extra quarter.

Another Beraisa rules that even if a purchaser insists that the seller weighs him ten Liters, one Litra at a time - the seller is entitled to weigh him the ten Litras all at once.

The reason for both of these rulings is - because to weigh three times a quarter of a Litra or ten times one Litra would entail a number of Hachra'os, when the purchaser is only entitled to one.

When the Tana of the Beraisa gives the measurement of the arm and the two strings of the scales with which one weighs metals, as twelve Tefachim - he means that the arm is four Tefachim and so are each of the strings which hold the actual scales.

The minimum length of the 'Nefesh' (the metal tube that runs from the ceiling to the arm, through which the cord that holds the arm [the 'Lashon' runs]) is - three Tefachim.

And the scales must be at least three Tefachim from the ground.

The reason for these two sets of measurements is - to prevent the scales and the arm from touching the ground and the ceiling (respectively) in the course of the measuring (thereby messing-up the measuring process).

The scales of wool-merchants and glaziers must be at least two Tefachim from the ceiling and two Tefachim from the ground. The size of the arm and the two strings is - nine Tefachim (three Tefachim the arm, and three Tefachim each of the strings).

The size of the arm and the strings combined of a storekeeper and of a private person is six Tefachim. The minimum distance from the ceiling and the floor respectively is - one Tefach.

The scales of a silver and gold-smith must be at least three finger-breadths from the ceiling and three finger-breadths from the floor. However - the Tana does not know the length of the arm and the two strings.

When Rebbi Mani bar Patish says (with regard to the scales) 'Just as they said concerning the Isur, so too, did they say concerning Tum'ah', he means that - whatever is the Shi'ur of the various parts of the scales as taught by the Beraisa that we just learned, is also the Shi'ur that renders them subject to Tum'ah.

We query the need for his statement however, from a Mishnah in Keilim, where the Tana states that - the string by which the scales of a store-keeper and a private person hangs from the ceiling is subject to Tum'ah if it is a Tefach long (rendering Rebbi Mani's ruling superfluous, because we assume that the same ruling applies to the different parts of the scales [see Rashash]).

We reconcile Rebbi Mani with the Mishnah in Keilim however - by pointing out that the Tana does not discuss the arm of the scale or the short strings (which are attached to the scales themselves), and which Rebbi Mani bar Patish comes to complement.

The Tana forbids scales of tin, lead, Gistron (a mixture of metals) or any other kind of metal - because they erode.

Besides glass, one may make the scales - out of stone.

Another Beraisa forbids forming a smoothening-rod out of ...

... a pumpkin - because it is too light to enter the pile (in which case it removes too little [so the seller loses out]).

... metal - because it is too heavy, and removes too much (causing a loss to the purchaser).

The smoothening-rod may not be formed in such a way that one side is thick and the other, thin - because that indicates that the owner uses the thin end (which enters deep into the produce to smoothen it well) when selling, and the thick end (which does not enter the produce properly and cannot therefore smoothen it) when buying.

One should use a rod - that is either thin or thick at both ends (depending on the Minhag).

When the Tana says that one should not flatten the heap ...

... in one go - he means that one should not smoothen it in one go quickly, because then the job is not done properly and the seller loses

... little by little, he means that he should not smoothen it too thoroughly, bit by bit, because then, he will smoothen it excessively, causing the purchaser a loss.

One should smoothen the heap - in one go but gently, or in two go's, half at a time.

Rabban Yochanan ben Zakai was in a quandary whether to teach these Halachos or not. Perhaps, he thought, one should ...

... not do so - because it puts ideas into the heads of the swindlers

... nevertheless go ahead and teach them - so that the swindlers should not assume that we are not aware of their tricks.

He decided to teach them after all, says Rav Shmuel bar Rav Yitzchak, based on the Pasuk in Hoshe'a - "Ki Yesharim Darkei Hash-m, ve'Tzadikim Yeilchu bam, u'Resha'im Yikashlu bam" (The ways of Hash-m are straight [and they must be taught at all costs, in order that] the Tzadikim go on them, and the Resha'im [let them] stumble over them').

The Pasuk in Kedoshim writes "Lo Sa'asu Avel ba'Mishpat, ba'Midah, ba'Mishkal u'va'Mesurah". We know that "ba'Midah" refers to the measuring of land and not to that of liquids - because 'Mesurah' is a liquid measure.

The Torah is coming to teach us ...

... here (with the word "ba'Midah") - that one may not measure for one partner (or brother) in the summer and for the other one in the winter, using the same measuring-rope, since the rope contracts in the summer and expands in the winter (according to Rabeinu Chananel, it is the ground that contracts in the winter and cracks and expands in the summer).

... when it writes "ba'Mishkal", which means literally 'with weights' that - one is forbidden to tip ones weights with salt (to make them heavier [see Tosfos]).

... when it writes "ba'Mesurah" (which, as we already explained, refers to the measuring of liquids) that - one may not pour the liquid into the purchaser's containers quickly, since that produces froth (which detracts from the required amount of liquid being sold).

'Mesurah' is - one thirty-sixth of a Log (a sixth of an egg-volume).

We learn from 'Mesurah' - that if the Torah is particular about cheating someone by an amount of less that a hundredth of a Lug, how much more so when it comes to larger amounts ... a Hin, half a Hin and a third of a Hin ... which will cheat the purchaser of larger amounts than that.

There are ...

... twelve Lugin in a Hin.

... four Lugin in a Kav (since there are three Kabin in a Hin).

The smallest measures in the list are Tomen and Uchla. Uchla will be dealt with later. Bearing in mind that it is also an eighth of a Kav, a Tomen is equivalent to - half a Log (or three egg-volumes).

Rav Yehudah Amar Rav forbids keeping a short measure in one's house - even if one designates it to use as a chamber-pot (since it can always be washed out and used once again, perhaps momentarily, for measuring).

Rav Papa restricts the prohibition to two conditions, one of them that it is not a place where the king's inspectors do not stamp the weights and measures (because if it was, the purchaser would not agree to the seller using them to weigh his purchase); the other - that the inspectors do not walk around constantly checking the weights and measures (because if they would, he would be afraid to use faulty weights or measures).

We reject the second condition however - on the grounds that sometimes, the purchaser comes to buy on Friday afternoon in the middle of the Shabbos preparations and, in the rush, the seller knows he can get away with using a faulty weight without getting caught, or it is the purchaser himself who, in his haste, fails to realize that the measure is faulty.

A corroborating Beraisa - also forbids keeping a weight that weighs more than it ought to in one's house.

The current Beraisa lists the solid measures that one is permitted to keep in one's house: 'Sa'ah, Tarkav, Chatzi Tarkav, Kav, Chatzi Kav, Rova, Tomen, Uchla va'Chatzi Uchla'. There are - six Kabin in a Sa'ah.

The Tana omits ...

... Chatzi Sa'ah - because that is equivalent to a Tarkav (two Kabin plus one Kav [which is already mentioned).

... Chatzi Rova - because that is equivalent to a Tomen, which is an eighth of a Kav.

We know that the Tomen is an eighth of a Kav, and not of a Log - because it follows 'Rova' which (as opposed to Revi'is, which refers to Revi'is ha'Log) is a Rova ha'Kav.

Three egg-volumes constitute ...

... a Tomen, one and a half egg-volumes ...

... half a Tomen.

The Tana presents an Uchla as a fifth of a Revi'a (Rova) - meaning a fifth of a quarter of a Kav (which is equivalent to a fifth of a Log).

This constitutes - one and a fifth egg-volumes.

The difference between a Chatzi Tomen and an Uchla is - three tenths of an egg-volume (one and a half and one and a fifth-volumes, respectively).