If the tube is shifted mesially and the object in question appears to move distally, it lies on the buccal aspect of the reference object. These relationships can be easily remembered by the acronym SLOB: same lingual, opposite buccal.  Thus,If the object in question appears to move in the same direction with respect to the reference structures as does the X-ray tube, it is on the lingual aspect of the reference object. If it appears to move in the opposite direction as the X-ray tube, it is on the buccal aspect. If it does not move with respect to the reference object, it lies at the same depth (in the same vertical plane) as the reference object.Ref: ORAL RADIOLOGY Principles and Interpretation, Stuart C. White, Michael J. Pharoah Edition 7 page no 88