Good on you! However, most PIs aren't like this. Their preparation is half-assed at best, and even then begrudgingly so. Thanks for taking the time and actually trying to do something. It's funny, in the ivory tower the word 'professor' has changed it's meaning somehow in the last 25 years or less. They think it means something like manager/grant-writer of grad students you get to boss around (and at least at some places, sexually harass with impunity). However, the rest of the world is still on the old definition of teacher/mentor/disseminator-of-knowledge. It's real strange to see these two ideas mix and the PIs come out on top, oddly.

Also, make sure to never ask:"Ok, now does that make sense?" after going through some real crazy math or something. It makes us feel real dumb when you do that and we then can't ask questions about it. Many PIs do that and it ticks me off to no end. It's like they really don't want to teach at all or have us interrupt their flow in any way.