Recently I found a 4-bladed easel buried in a pile of stuff in the closet at my school's photography classroom. Normally we use the little quick easels that have preset masks in standard sizes. This particular 4-bladed easel is not a high quality easel by any means, but I would still like to use it. However, I am having trouble lining up the paper with the spot that the blades will fall upon. How would I go about making sure that my borders are even?