More then likely the arms are bent a little. Don't shoot for zero bubble but the bubble to be at the same place over each foot. You can also put a washer under the one end of the level to compensate for the bend. If you move the level all the way back where the arm is attached to the plate I think you will get a different reading, closer to zero. I would also back off the pallet locator so the arms are not bouncing over it shaking the level.