I have a question along your same lines. On your question, yes the unit will automatically read the card regardless of which of the two card slots you put it in(left or right). You can go into the the navigation menu and override which slot to read but the unit will automatically pick the slot you have put the map chip into when it's in "automatic" mode. Also you will only have the choice of left or right if a card is in those individual slots. IE: if you go to the menu when your Navionics chip is in the left slot you will only be given the choice of "automatic" or "left". I only have one card so it works automatically. This feature(I believe) is for choosing a chip when you have more then one chip plugged in. Mine works great BUT I purchased the Navionics Platinum South chip and along with the contour maps it also has 3D and satellite imaging. My 898 goes directly to the contour map but I have no idea how to access the 3D or satellite imaging. Hope this helps with your question and someone else can post how we access the other functions that are on the Navionics lake map chips. Neil