Keep in mind that WW sells scales. I think they make them off a bit knowing there will be a difference to get you to buy it. Just my little conspiracy theory!
Consistancy is all that matters. Just pick one that's the official scale and go with it. It's the direction it moves rather than the actual weight anyway.
I hear ya, though. I never can figure out what I really weigh, what size my pants are or anything. Hehe. I just know that the scale I have is going down and my pants are bigger (more than just stretching them in during the day). It could drive a completely sane woman off the deep end!