I used to think that it had something to do with gauge, but gauge can vary throughout a project. I bought a hank of Mountain Colors "Bearfoot" the other day, which I assume is a self-striping yarn, and it said "between so-and-so and so-and-so stitches to the inch." (I can't remember the numbers.) This would suggest that gauge isn't all that important. So now I'm confused; how do these yarns work?