Take a pic of the model number and I’ll conf it for you 100%, however I’m pretty sure the round thing at the bottom of the gearbox is the US2 transducer. It’s a transducer built into your trolling motor so if you want a bow mounted graph you plug it into this transducer and you don’t need to have the complex and potential issues of having multiple transducers on your transom. I don’t personally have it but I know what it is and I know it’s an expensive option. Obviously for it to work your trolling motor must be deployed but if your fishing on the casting deck it will be.