What you end up doing really is stitching in the ditch from the front to the back. There is a package that comes with it if you order the complete system containing a binder foot with 4 fences. The fences are numbered 1-4 from no loft to high loft batting. You put this on your machine under the needle on the throat plate and a zip bind tool that you adjust to your quilt binding edges.(I'm still working with this part to get it adjusted just right-depending on the thickness of your binding). The two work in tandem-takes quite a lot of practice to adjust this zip bind tool. If you want to practice with this I'm sure it would help-the outcome is to be the amount of binding you've turned to the back side is just perfect to stitch in the ditch from the front and have enough fabric turned to the back to have a straight stitch-in-the-ditch-not to be going on the binding-off the binding-on the binding-off the binding. Does this make sense? You really need to to to Martelli.com and watch the tutorial.