1. The Gemara explains the source for measuring Techumin with a rope of 50 Amos.
2. The rope must be made of linen.
3. Rav Yosef says that there are two other sources that mention that a certain type of rope must be used for a certain purpose.
4. Only an expert may measure the Techum.
5. Even an Eved (or Shifchah) Kena'ani is believed to say where the border of the Techum lies.
A BIT MORE
1. Rava: It is derived from the verse, "And its width is 50 with 50." The extra "with" ("ba'Chamishim" instead of just ""Chamishim"") hints to measuring Techumin using a rope of 50 Amos.
2. Even though metal chains would measure more accurately, the verse in Yechezkel implies that the rope should be made of linen.
3. The rope with which the Parah Adumah is tied be made of reed, while the rope used to hold up a Sotah's clothing after it is torn is made either from a willow that has been stripped of its leaves or from the fiber of a palm frond (see Rashi).
4. The Mishnah explains the circumstances in which we believe him when he says that there is more space in one area and less in another.
5. Although only an expert may actually measure the Techum, the Chachamim were lenient with regard to who is believed to attest to where the Techum lies (after it has been measured). This is because the Chachamim were generally lenient with regard to the laws of Techumin.