The BDC dial works on the ballistics of the caliber. It is engraved in 50 yard increments. You only need to know the yardage and dial it in. So no it is not necessary to have the scope on high power - it is the same at all powers. You do need a range finder or the ability to know the range. Hope this helps.
Thanks guys, sent Leupold a E mail to tech services and it showed it might take up to 2 weeks for a reply. Its almost impossible to get a call thru out there now.