There's also the occasional teeth-curling screech when a fingernail or little bit of hard matter in the chalk scratches the board. Even at that though, I think I prefer chalkboards.
I teach math, and just as some people cannot taste the bitterness in Brussels sprouts, I'm not affected by the fingernail-on-blackboard noise. I find it very useful for taming a class of wild freshmen, though. I only have to do it once.
"It finds the correct delta or else it gets the noise again."
