The Physics of Putting

I'm fairly sure you're not supposed to walk along your putting line in golf because it can subtly change the curvature of the green. I know you're not supposed to step within a foot or two of the hole, and there could be enough break in that distance to make a putt miss.

I'm not sure if it's simply etiquette or if there is a little-known rule that penalizes you for doing so, but using your feet to detect a break seems, to me, to be a questionable practice in anything approaching a serious game.

OK, so what _is_ the method?