Your latitude and longitude will always be where your GPS antenna is whether you are using a point one, lcg or the internal antenna on the unit. If you put your sonar transducer on a 50 mile long cable, drove the transducer to the lake and dropped it on top of your favorite brush pile and started marking waypoints its still gonna show your boat sitting in the garage on your map because thats where the GPS antenna is. And your waypoints will be in your garage 50 miles off. The only way that graph knows where in the world it is, is by triangulation between your GPS antenna and 3 or more satellites. Therefore the further your GPS antenna is from the sonar transducer, the further off your waypoints will be from correct. If your antenna is directly above the transducer it doesnt matter how you mark it, they will be accurate.
