Humminbird HELIX 5 SI GPS Operation Manual page 34

Use Bottom View to select the method used to represent bottom and structure on the display.
See Sonar Menu to set the Bottom View.
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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What's on the Sonar Display