I agree with Scoot.
If, in rehearsal, you can not find something to do . . . at the very least paying attention, then perhaps you should find another line of work.
Being present, alert and paying attention to what the director is doing and the actors are doing is very important in this profession, especially if you are going to have some hand in maintaining the show - which may not be the case.
Between taking notes, working on the report, trying to figure out who is going to move the 7th chair in the scene change, how someone is going to make the quick change, there is always something to be occupying yourself.
If you have nothing else, the least you can do is pay attention to what is going on.
Think of this way, you are the actor, working hard on a scene, you looking up, and there the stage manager is bored to the point they have to doodle to pass the time. How would that make you feel?