Hon, you have to choose one scale and stick to it. You can't go back and forth. If you're going to keep the new scale, then forget about the old one and stop weighing on it.
You'll need to adjust your ticker to the difference between the two scales--because when you switched scales, you didn't "lose" 6 pounds.
So, give yourself a lower start weight to calculate your loss overall.
All this assumes that there isn't anything wrong with your new scale--which I don't think there is. I imagine that your old scale is messed up in some way (no pun intended).
Get a ten pound bag of something, like sugar or flour or pet food, etc. Weigh it on both scales. The scale that says closest to ten pounds is the more accurate one. To be more accurate in your weight range, weigh yourself on both scales with and without holding the ten pound bag. The scale that gives you closest to a ten pound difference is the more accurate one.
Jay