My friend has the 859 and can't seem to mark waypoints without a SD card. He should be able to with a card right? He has a Navionics card in it right now in read-only and it gives him a read-only error message when he presses mark. I tried looking for the map card slot select but didn't find it in the menus. Is there something I'm missing? He does have a couple of waypoints on the units but it's not letting him add anymore right now. Thanks.