The black box is an aiming point, if you care to use it. It works best with low power scopes 12 to 18 powder for me. Its to big for my 36 power. You can put the crosshairs in the center or on a corner.
http://benchrest.com/showthread.php?69832-Aiming-Point The " mothball" is the center small ring. Dont shoot out your aiming point.