Pick a scale. Use it in the same place (Trust me, moving it around the floor is bad) at the same time (mornings are best) in the same (approximate...) clothing or non-clothing (yup..nekkid)... and don't worry what the other ones say. The actual number is not that important (a shift in a few pounds up or down really isnt what matters) -- what is important is consistency, so that you can track the change you're making.