Teaching/instructing

The skill either to teach someone some skill or knowledge that one already knows very well or to explain some complex circumstances in easy words.
Bonuses and handicaps (especially useful for the master): characters can only raise another character's skills by one or two skill points by teaching them. The teacher must have a skill level of at least 85 in the skill that is to be taught and a lesson takes about a week.

The starting value is: 3 * I + C