If you have the smallest size rotary cutter, you can easily cut along the top of the ruler with it. If you don't be careful if you use a "regular" size rotary cutter. I wasn't careful enough, and had a nick into one of my next wedges. Had to do some unstitching and replace that piece.
Don't worry, it really isn't hard and lots of us have made them now, so we're here to help!