I think a way is to get a level door frame, (target sight only method) place your sight bar level with the door frame, adjust 2nd axis there, point your scope at the ceiling and check it again. It would be wondering if doing it at full draw will have that much difference than doing it in a vice. If you are shooting to the left on downhill shots, you need to turn the level (sight body) away from you and if you are shooting to the left on uphill shots the opposite is true. @Stapher is right with his thought.
Sam
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If this is your first time of entering the hunting field, picking the
barnett crossbows as your hunting tool is a smart decision that you can make.