Humminbird LCR 3D - Manual (Page 23)

2. Setting Depth Range;
Factory setting: AUTOMATIC
When you turn the LCR 3D on, it finds the bottom,
sets the ideal Depth Range, and automatically adjusts the
range as the depth changes. In this "Auto Depth Range"
mode, the bottom is always displayed for easy-to-
understand readings (and AUTO appears at the bottom of
the screen).
If you prefer, you can turn Auto Depth Range off.
Select DEPTH RANGE, press ENTER, and adjust the
Depth Range with the UP or DOWN arrow key. You can
set Depth Range up to 99'.
In this "Manual Depth Range" mode, the 3D view
shows a flat grid if the bottom is below the depth you have
set.
In the 2D view the bottom will simply not be seen on screen.
3. Enabling Bottom Alarm;
Factory setting: OFF
The Bottom Alarm lets you specify the minimum
depth you want to maintain. To use it, select BOTTOM
ALARM; then, press the ENTER button to activate the
alarm, and the UP or DOWN arrow key to adjust the depth
at which the alarm will sound. A Bottom Alarm indicator
and the selected depth are displayed when this function is
on.
While Bottom Alarm is on, you'll hear a continuous
chirping sound when the bottom directly under your boat
gets shallower than you defined. This is very handy for
alerting you to shallow water or helping you to maintain
position over structure.