Tearing printmaking paper easily

This is so simple it's brilliant. I saw this in action at Ron Pokrasso's workshop that I took earlier this year (post about the actual workshop here). He marked off tear lines for a 1/2 and 1/4 sheet of printmaking paper and indicated where to line up the edge of the paper. I replicated this by drawing vertical lines at the 11 and 15" marks, making paper tearing super quick! I'm excited to be printing with some friends next week--Catherine Small and Jill Alo--and so I am here today just refreshing my memory on monoprints as well as the awesomeness of Ron Pokrasso.