It might be called "sensitivity."  I'm using the old flasher terminology.  Old habits...

No problem. I really like the unit so far. I'm still learning how to use it.

On mine the 2d is called sensitivity and the 3d is called contrast. 

The first recreational fresh water sonar units were flashers followed by Lowrance paper graphs that transitioned to liquid crystal sonar that had limited pixels, then color.

It was the paper graph era that I learned to read sonar by looking at the paper rolls following a days outing. Paper graphs had very clear print out depending on the power the unit had and power upgrades were a matter of changing circuit boards. We learned target separation by reading secondary echoes to determine fish from structure, everything was in black, white and shades of gray.

Color changed how we read sonar and target separation was instant. Today's sonar interpret signal strength from programmed data, not actual signal returns that can give a false reading, still easier then studying the paper Rolls. If you haven't lived through the paper graph era you missed out on reading sonar, buying chases of paper rolls, changing stylist and drive bands, vacuum out the carbon dust, so much fun.

Tom