I dont think theres a thing you CAN do with it. The GPS on these Humminbirds leave a LOT to be desired. I LOVE my unit and I wouldnt trade it for ANYTHING...except one with a faster more accurate GPS. Its not an issue until you are going SLOW or trying to pinpoint a pile or something.

I can turn mine on in the boat in the yard and it will jump all over the place and tell me I am going 2mph then 1.7, then .9. I have a 798SI with internal GPS and thought about getting the external one. But I see more and more guys having the same issues with their $200 external antennas too.

Tighten up humminbird!!