Hopefully you know what I am talking about, it is a little green submarine looking thing they sell at Gander. You cast it out with your pole and it sends a reading back to a unit on your pole to show you the bottom structure and depth and any fish in the water. I bought it last summer before I had a boat and still use it at lakes where boats are not allowed. I think it is great for telling what the bottom looks like and looking for structure but the fish finder is a little off. It will tell me there are ten fish piled up together in a couple of feet of water and I will check the area and there is nothing. It is probably picking up minnows or fingerlings, but is there some way to separate out small, small fish from catchable sized ones. Does the sensetivity on these units go with the bigger number or the smaller number? I lost the directions when I moved. Has anyone else used these or like them?