from what I remember of the one I had the C map just went in and it worked, end of story. Except that the waterproof unit didnt do light rain, heavy rain or anything at all dampish. Saw sense in the end and binned it! Shame really as it was a nice display, trouble was a bit of rain and it would go off on a mission through all the charts in its memory...except the one where you happened to be. Best of luck with it