The Geonav 6 Sunshine - When it's in Dark Area

[filaviasail]

Sorry or my english
. I have 2 memory or cartridge for Navionics Geonav Sunscine 6: 1 is
ed and the gulf of Mexico Carabiem...
- the first of the Mediterranean and I think I take you to Gibraltar or just after
- the other cartridge in the Caribbean or Central America or the Gulf of Mexico.

If i am crossing the atlantic in a zone taht is out of the Naviobnics catriage charts wich info the Geonav will give me?
I need at list to know the error of my course, do you know if the istrument will give me other infos?
I have tryed to take the cartiage of the Geonav but the only info i see is the distance from the poin i wont to arrive.
Ciao Gianni