I have long believed in picking a scale and sticking to it.
My bathroom scale never agrees with my doctor's scale never agrees with my Wii scale. So I choose to "believe" my bathroom scale because it is the one that I use most often.
It's not so much that I truly believe, but that I use that as my point of reference. As long as my point of reference number gets incrementally smaller each time I get on that scale (don't I wish?) I'm a happy gal.
Of course, I only get on my bathroom scale second thing in the morning. First, I have to go to the bathroom. After three meals and 8 glasses of water, I'm pretty sure the resulting number would not please me. And it's all about me, doncha know?