Think of the arrows path(centershot of the bow)as another plane that the bubble has to be SQUARE with.If that plane isn't maintained on a square plane with the bubble,you will hit left or right and lowof the intended spot.


That is all a level does,reads square,when it gets rotated downhill,it must remain square with the intended plane(in this case,arrows path)to read correctly.


Give it some time to sink in,not really all that difficult.[8D]