Careful on the lowrance products as they have told several folks with problems that lowrance does not support any unit that is over 2 years old. They may offer U $250. or similar amount for your unit on a trade in buts that's it. Heard of a lot of 520 problems. Yes these comes from a unhappy HB 997 owner of 3+ years, yes Si is great but GPS needs a seeing eye dog. Yep that MOB-man over board button couldn't find its way back in a Goldfish bowl.