lmorin:I also use mechanical pencils. Bought some from Staples that have no metal parts. Forget the price, but were very cheap--cheaper than regular wooden pencils. Had to sand and flatten the pencil shaft in order for it to fit in the pencil holder on the slate.
I don't have a power pencil (like power steering/brakes) like that but I do have a manual one.... wooden pencil and dive knife.