Why did the rabbis of the Talmud use approximate weights and measures, such as k'zayit, k'betzah, revi'it, k'dei achilat pras, amah, etc. , which caused disagreements among later Sages as to what they meant, when precise units were readily available in Greek and Roman times ?
Some say they wanted to relate the quantities to everyday matters (olives, eggs, loaves of bread, etc.) so the average Jew would understand. But they could have used BOTH. Surely they were aware that later generations would have a problem understanding precisely. And sometimes they DID use precise Roman measures.
The only logical conclusion is that they did not want to set the matter in stone, but INTENDED it to be approximate. (Of course, they did not anticipate that genetic manipulations could produce giant olives, but that's another matter. :-) )