The HDS units are great depth finders. My advise is get out on the lake and use it, when you find something drop a line down and bump around. I have a gallon zip lock bag with the owners manuals, screen cloth and a small note book in the dry storage in my boat. I have the basic settings for the unit and short cut notes written down, this way if I get it out of whack I can go back to my initial settings easily. If you really want to know whats down there buy a LSS-1 or 2.

There are two great forums on Bass Boat Centeral, Lowrance/Garmin Sonar/GPS and Lowrance Image Interpretation. You will find a ton of information there.