Looking to add another finder. I have been looking around for a couple of weeks now. So my ? Is what is the diff in the HB 899 and 999 is it just screen size and what else do I need to know before I make this purchase in the next couple of days. The new unit will replace a 597ci hd di unit I bought from Brian last year. And moved to the bow where an older 535 is located now. Once the 535 comes off anyone that wants it they can have it I will be giving it away. Just want to know the diff In the 2 units because this is something that I don't want to buy again so want to get this right the first time.