Avi – That is why I deliberately wrote “the upper arm” – I didn’t want to get into anything controversial. When I wrote that the girls were wearing short sleeves, I did not mean that the elbows were showing or even less than a tefach above their elbows – I mean that their “upper arms” were clearly showing regardless of the possible definitions of “upper arms”. In other words, they were wearing cap sleeves.
btw, this idea of adding a tefach is not at all poshut. I believe it is a misconsception. In the non-BY seminaries, many people (at least the students) used to think that was the case, and many of the schools allowed it. However, over the last 30 years, people have begun to realize that it’s a problem, and I think that most of the seminariess no longer allow it.
It seems to be based on the halacha that b’dieved a man can say krias Shema in front of a girl who has less than a tefach exposed, but that does not mean that she is allowed to have that exposed l’chatchila.
In any case, it would be less than a tefach, not a tefach. And when girls wear sleeves that are just under a tefach above their elbows, more ends up showing since their sleeves are not glued to their arms. That is also the problem with having sleeves that are above their elbows even if one holds that the elbows themselves don’t have to be covered.