Sticking my nose in where it don't belong. ;-) But that's never stopped me before. ;-)

First "I are not a teacher". At least, not in any formal sense of the word. Second, some would say "I are not a programmer". I don't listen to those people.

In spite of the common "in computer graphics Y goes down", does that make sense to new learners? I've gotten used to various coordinate systems, but the first time I had to work with graph paper and plotting (and, for that matter, maps) one goes "up" ("north", "forward") for Y. Then again, maybe the average learner isn't quite as flexible these days, and telling them after they've gotten used to a system that they have to flip everything upside down and backwards isn't a great idea. I attribute my own flexibility not to any innate ability but rather to learning during a time when architectures OS's and languages were changing fast enough that there wasn't time to become set in one's ways.