bumper,
I don't owe a garmin but on my eagle's you have to cut off all the fish id's, fish tracking, fish alarm, to see the arch's. Also may want to put it in the manual mode instead of auto. You may want to check the angle of the transduce and make sure its shooting straight down if its angled it will not show the complete arch. I'm sure there some folks that know way better than I but you might try these that I've found to help me.