Bonnie's method is great! I never "measure" for a border. It's easier to me to lay it out than trying to make sure a measuring tape doesn't move. Since I've been doing it this way, I haven't had any wavy borders. My sister is just learning to quilt and was having border issues. Once she started doing it the way I do, no more problems! I wouldn't give it to a longarmer with wavy borders. Good luck!!