One of the best explanations of the perspective rulers in Manga Studio EX 5.0 I’ve ever watched.  I sure wish I’d had this handy when I was going crazy trying to figure out why my lines would only snap to one of my vanishing points (explanation at 0:54 :P). ElectricAlice also has a wonderful perspective tutorial for comic artists here: http://electricalice.tumblr.com/post/68701008868/10-typical-perspective-errors