Prism99 is exactly right....I assume you are using a cutting mat - the other way to look at it is that both folded edges (the center fold that is lying against the selvage, and the 'second" fold you mention above) are perfectly parallel. If not, you can get a heck of a V in the middle of each piece. Been there, done that, before i learned to make SURE the piece was perfectly "squared up" before cutting.