Garmin manual implies that you can back up and restore waypoints to a data card. 2 cards came with 2006c when I purchased boat. Top card is "Bluechart." Bottom card is labeled "GMZ502L." I don't have a clue what "GMZ502L" does, other than perhaps it is a data card to backup waypoints. Has anyone ever backed up to and restored from a 2006 data card?