I don't want to lead anyone astray but wanted to ask if there is anyone out there who doesn't measure?
I never do and have not had any problems with waves.
I simply make sure that the quilt top feeds without stretching and gently, and I mean gently, tug on my border strips to eliminate any "after stretch" as fabric cut on the width has a more stretch than fabric cut from the length (according to some). The other thing I do is baste all around the pieced quilt before adding the borders to stop any additional stretch.
CRO, maybe cutting the fabric on the length would be helpful to avoid waves although most times, one doesn't have that much fabric unless it's leftover from a back.