Depth Lines (Advanced); Noise Filter (Advanced) - Humminbird 688ci HD DI Operation Manual

Depth Lines divide the display into four equal sections which are separated
by three horizontal depth lines. The depth of each line is displayed along the
depth scale. You can turn Depth Lines On or Off.
Noise Filter adjusts the sonar Noise Filter to limit interference on the display
from sources such as your boat engine, turbulence, or other sonar devices.
The Off setting removes all filtering. Low, Medium, High 1, High 2, and High 3
settings add progressive filtering of the sonar returns. High 1, High 2, and High
3 are useful when there is excessive trolling motor noise, but in some deep
water situations, the High settings may actually hinder your unit's ability to find
the bottom.
Depth Lines
(Advanced)
Settings: Off, On; Default = On
Depth Lines
Noise Filter
(Advanced)
Settings: Off, Low, Medium, High 1, High 2, High 3;
Default = Low
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Depth Lines
Sonar Menu Tab