Heading; Sonar Tab; Water Type; Depth Number - Garmin Fishfinder 320C Owner's Manual And Reference Manual

• Heading — lets you select the reference used in calculating heading information for the the Bearing,
Compass, Course, and Track Advanced Data fi elds (pg. 14). 'True' will display data with reference to
True North. 'Magnetic' will display data with reference to Magnetic North using the magnetic varia-
tion value received in the RMC NMEA sentence (see pgs. 3-4).

Sonar Tab

Allows you to set up initial settings and calibrations. The following settings are available:
• Water Type — since sound waves travel through 'Fresh' and 'Salt' water at different rates it is
necessary to select the 'Water Type' to ensure accurate readings on the unit.
• Depth Number — controls the effi ciency of the digital depth update rate. 'Fast Sonar Update' will
update quicker and is recommended for low-noise, deeper water (>50 ft.). 'Auto' is best for shallow
water or high noise areas, will have a slower screen update, and is best used if you travel a wide
variety of depths.
If the unit is unable to track the bottom for any reason, the digits in the depth window will
fl ash on and off to alert you that the unit is not tracking the bottom.
• Automatic Scroll Speed Limit — automatically adjusts the Scroll rate (see pg. 12) to the speed
of your vessel (if equipped with a speed sensor or receiving GPS NMEA input). Entering your maximum
cruising speed will produce a 100% scroll rate when you reach that speed. One half of that speed
will produce a 50% scroll rate, etc.
• Keel Offset — allows you to offset the surface reading for the depth of a keel. This makes it possible
to measure depth from the bottom of your keel instead of from the transducer' s location. Enter a
positive number to offset for a keel. It is also possible to enter a negative number to compensate for a
large vessel that may draw several feet of water. The 'Keel Offset' will be refl ected in the depth read-
ing.
• Transducer Type — this will not appear when in Simulator Mode. Allows you to specify what type of
transducer you are using. 'User Defi ned' is for future use and should not be used unless instructed.
• Calibrate Water Speed — this will only appear if you are using a speed-capable transducer/sensor.
Calibration is required to ensure that the Water Speed displayed on your unit will be accurate. The
Unit Operation
Main Menu Options
Main Menu - Sonar Tab
Transducer at Surface
Enter (+) positive
number to show depth
from bottom of keel
Transducer at Bottom of Keel
Enter (-) negative number to show depth
from surface
19