Kelim, Chapter Seventeen, Mishnah Nine
1) The cubit of which they spoke is one of medium size.
2) There were two standard cubits in Shushan Habirah, one in the north-eastern corner and the other in the south-eastern corner.
a) The one in the north-eastern corner exceeded that of Moses by half a fingerbreadth, while the one in the south-eastern corner exceeded the other by half a fingerbreadth, so that the latter exceeded that of Moses by a fingerbreadth.
3) But why were there a larger and a smaller cubit?
a) Only for this reason: so that craftsmen might take their orders according to the smaller cubit and return their finished work according to the larger cubit, so that they might not be guilty of any possible trespassing of Temple property.
Section one: The measure of a cubit is a standard measure found in connection to many halakhot, including the issue of carrying on Shabbat (see Shabbat 11:3).
Section two: Shushan Habirah is the capital of Persia, as mentioned in Esther. There was a place on the eastern gate of the Temple with a drawing of Shushan Habirah (see Middot 1:3). At this place there were two rods which were used to set the size of the amah, the cubit. The rod in northeastern corner was shorter than the other rod by a fingerbreadth. The cubit that was normative in the days of Moses was right in between the size of these two rods one fingerbreadth larger than the small rod and one fingerbreadth smaller than the large rod.
Section three: The mishnah now asks the logical questionwhy have two different sized cubits? The answer has to do with the artisans who work for the Temple. These craftsmen would take their orders using the smaller cubit, meaning they would receive material from the Temple based on the smaller measure. Then when they made their products for the Temple, they would return them based on the larger measure. This ensured that they did not transgress the prohibition of trespassing, meaning illegal use of Temple property. In this way, the Temple could be sure that the craftsmen would make sure they used every bit of material they received from the Temple.