White Line

Whiteline, which Lowrance refers to as Greyline, changes the Way a machine displays the bottom echoes. With Whiteline activated, the bottom will show up as a thin black Line under which varying depths of white or gray indicate strong or weak echoes. This makes it easier to determine >Bottom Hardness and differentiate between bottom and objects close to the seabed. Aside from giving a view of rocks and obstructions, this can make a big difference in your anchoring decisions and techniques.

Furuno also describe it intended use to discriminate Fish swimming near the bottom from the bottom itself. The top edge of the sea floor is displayed in white to clearly show structures. This helps to distinguish weeds and bottom Fish distinctly form the bottom itself.