One of the world records for a standing high jump is about 6' (1.82 meters, IIRC). So, for that, I would give it a TN of 30 at the very least.
So, that would mean a TN of 5 for every foot of distance to be covered in a standing high jump (note: if trying to reach something above one's head, a character's overhead reach is likely to be about 1/3 of his height. (i.e. a 6' character has a normal reach of 8', so if he is trying to reach a ledge 12' off the ground, that means he only has to jump up 4' (12' - 8' = 4').
Hmm.. as for armor -- good question... the way that the rules are currently written, they don't affect the acrobatics skill at all (which is what would be used for jumping - it or the Athletics skill). I am thinking that perhaps those 2 skills should ALWAYS be affected by the Armor Penalty, even if the character has training... (just as encumbrance would do so) or perhaps have the AR act as a modifier for the skill....
Will have to give it some thought (don't expect an answer to be in version 0.4)
