Take the new one back and rely on the old one, but put it on a level surface. Mine is in the carpeted bedroom (the bathroom is too tiny) and it's on a piece of plywood that is just an inch or so bigger all around than the scale. If you still think the results are erratic, go rebuy the new scale. I'd try the plywood under the old scale first. If I move my scale from room to room, where there are different thicknesses of carpet, I can get as much as a 20 pound difference. The thicker the carpet, the less I weigh!
Life style change started on Jan 13, 2011. I was going to lose 100 pounds by Christmas.
I lost 93 pounds by Oct 1, 2011 and am holding there for now. We'll see what happens.
New goal: To maintain at about 160
Final Goal: To decide if I need to lose more
Just Keep On Keepin' On