From SK:
My settings are very close to what this chart says however I constantly change my settings.
The chart speed always 1to 2 faster than boat speed, the sensitivity has to be adjusted according to the hardness of the bottom, harder bottoms require lower sensitivity & softer require high sensitivity.
The contrast sorta works hand in hand with the sensitivity it's no different than the contrast on a black & white tv to high it'll wash out to low it be to dark.
These three settings must be adjust for the area you're in. On my home lake I've pretty much got my units dialed in for the different areas but be prepared to adjust these three on the fly.
The best thing to do is go over a area with known structure with the screen spotted 1 to two faster than your boat speed (try 3mph boat speed & 4 on chart speed), once the structure is in the frame hit the direction button to freeze the screen, stop your boat & play with the sensitivity getting the best clarity & then adjust the contrast to adjust the brightness that's best for your eyes.
Wish I was closer to you I'd meet up to assist you.
One more very important thing is make sure your batteries are fully charged & you have good connections between your unit & battery. These units don't work with a flip on low power....