Running a new Humminbird 400+ pro angler fish finder. Worked the first three times out. Went out today and was reading 5-6 feet to high. Tried resetting to factory settings , no luck. Came home , with the boat on the trailer tried moving the settings to adjust sensativity.It reads correct at two feet from the ground , but had to move the settings by 5 feet to calibrate unit. Any idea's why the calibration is off ?Thanks , Bob