Always remember to try and go in as straight of line as possible for the best viewing. If you make turns it really changes how much ground is being covered on the out side as well as the inside. The inside will look much like your not moving or even moving back ward, depending on how tight the curve is and the out side covers the area on that side with increasing speed with distance out. In other words there is more distortion further from the boat than close.
I set the sensitivity on mine on the 455mhz mode to zero which is the auto mode. That way when you move over bottoms with different reflectivity it adjusts as you go along. For screen speed, I like to start out by running the scroll speed at the same number as miles per hour, then adjust from there. Too fast a scroll will make weeds and objects appear elongated along the path of travel. Too slow every thing will look more rounded, even long objects. Just remember that the distance out from the center line is for all intents and purposes, exact. Distances along the line of travel are a variable of scroll speed vs boat speed so when ever one or both are changed the distance represented on the screen top to bottom changes.
WarrenMN