Okay my wii fit scale sucks! I use it on carpet usually and when the bottom things aren't on the corners, it says I weigh 20 pounds less than I actually do. And when its on the rubber corner circles, the weight is apparently right, but it just changes a lot. Even if I weigh myself twice within one or two hours.
I was using a fancy digital scale at work and losing weight beautifully until one day I noticed that my weight varied by a bunch of pounds just by moving the scale a few inches in any direction. Ultimately i realized I really had no firm idea what my starting weight was (other than "very fat") or how much I'd lost (other than enough to fit comfortably into a smaller pair of jeans).
I no longer trust any scale that's on carpet. And I always remember to take any particular weight as approximate. (which isn't to say that I don't get excited every time the scale says I've lost weight and a bit down everytime it doesn't...)
