Assume you are mounting a new Terror with Bluetooth. The puck you are taking about is the heading sensor/compass. The instructions about the keel is to make sure you line the arrow up with the keel. This will ensure when you use SPOT LOCK JOG it will move the boat truly forward, left, right, or back according to the heading of the boat.As BCB stated try to mount it away from metals, or magnets if you have any at the bow.Mine is mounted at the bow on the carpet in the upper left (port) corner near the GPS antenna.Image showing the GPS antenna, cant see compass but its under the mount – see next imageImage showing the compassLast edited by Caldwellj on May 23rd, 2017, 7:25 pm, edited 1 time in total.