since i bought the unit i have noticed it off and on, on different bodies of water, that my sonar will read about 10 feet deeper than it really is. Watching the spitfire sonar i can tell it will be 8-9' deep, but the depth reading shows 18-19' feet deep. Once again i have noticed this on different bodies of water, and its started to bother me enough to seek out help. This is occurring while i am drifting with the current, breeze, or the trolling motor, so i know high speed is not the issue. Thanks in advance for any help guys!