[Gdeaver]

Is this an underwater ROV? If so you have another problem. The compass you're using is a 2 axis one. If there is any tilt the reading will be way off. For apps that tilt there are 3 axis compasses with accelerometers that can compensate and give good accuracy. There are models that are ready to go with an easier RS232 interface that would work better for this app. However, they are hundreds of dollars.