Yeah, Muon2 is correct - there is a type of overhead that does not require a transparent sheet - I assume that is what that is. A lot of classrooms (not all) are equipped with them. They're really cool because you don't have to make copies. If there's something in a book that you want to show to a class, you just put it on that thing.
Don't know about HS - probably depends upon where you go. I'm certain the old style ones are still around.
When I was in middle school there was a teacher who used a '60s era
slide projector.
Poll
