I understand about the dart for shaping. The pattern (McCall's M4745) can be adapted to single or double breasted. The difference is a wedge shaped piece of fabric sewn on. ( and more buttons, of course.) I am sure it can be used to adjust contour, as the dart does, but it looked funny in the drawings. We discussed simply taping the pattern pieces together to create a single panel, but then we saw the seam/dart on the sto bought one. Mercifully, I am not the one sewing, The One who is has plenty of experience and chops. I do wish I could get her to insert a little piping in all of those curvy seams on the back. Mais, ca c'est un peu du trop, je crois.