Humminbird 698ci HD SI Combo Operation Manual page 36

Use Bottom View to select the method used to represent bottom and structure
on the display. See Sonar Menu Tab to set the Bottom View.
What's on the Sonar Display
Structure ID™ represents weak returns
in blue and strong returns in red when
Sonar Colors is set to Original. If the
Sonar Colors palette is changed, the
Structure ID® will display the strongest
return as specified by the palette. See
Sonar Menu Tab: Sonar Colors for
more information.
WhiteLine™ highlights the strongest
sonar returns in white, resulting in a
distinctive outline. This has the benefit
of clearly defining the bottom on the
display.
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