Kelim, Chapter Seventeen, Mishnah Six
1) The egg of which they spokeit is one that is neither big nor small but of moderate size.
2) Rabbi Judah says: the largest and the smallest must be brought and put in water and the displaced water is then divided.
3) Rabbi Yose says: but who can tell me which is the largest and which is the smallest? Rather, it all depends on the observer’s estimate.
Section one: Concerning many halakhic measures, the egg is used as the standard. The egg to which these halakhot refer is an egg of medium size.
Section two: The problem is that it is not easy to determine what egg is of medium size. As a solution Rabbi Judah says that one should bring the largest egg and the smallest egg and place both in a bowl of water. The water that is displaced can be divided into two to determine the volume of the medium egg.
Section three: Even this method is not perfect, because it requires a person to know what the “largest” egg is and what the “smallest” egg is. In other words, there is no way to remove subjectivity from this. In the end, no matter what you do, it will always depend upon the subjective estimate of the observer.