I have never done scrapbooking before, so I'm a little clueless...OK, very clueless. I will be making boarding pass invitaitons, so I am going to purchase a paper trimmer and am trying to figure out which blades I need. I know I need the traditional straight blade, so I'm not worried about that. I would like my RSVPs to tear off and be mailed to me as a postcard. I've seen people mention perforating blades and scoring blades. It sounds like the perforating blade would be what I want, but what does a scoring blade do?