I bought two balances. A magnet kind and a bar kind. Both failed. As first I thought everything is going well. Got it to balance horizontally, but then I took out the plastic holder and flipped the prop from left to right, then it's not balanced anymore! I suspect the system itself is not even balanced. Depending on how I mount the prop, it will give a different result!! Sometimes, I get it to balance horizontally on one side, then rotate the prop to the other end and it's unbalanced! How can that be? How can it be balanced on one end but not the other? How do I do this??