GPSMAP 392/398/492/498 Owner’s Manual 81
USING SONAR > UNDERSTANDING SONAR
To calibrate the water speed:
1. Use the ROCKER to highlight Calibrate Water Speed, and
press ENTER.
2. Bring the boat to a cruising speed. Both the top GPS ground
speed and uncalibrated water speed appear at the bottom
of the calibration window. Note your top speed, stop the
boat, and press ENTER.
3. By default, the top speed automatically appears in the What
was your top water speed? field. If a ground speed is not
available, the top uncalibrated water speed is used instead.
If the new speed is correct, highlight OK, and press ENTER.
If you want to manually enter a calibration, press ENTER on
the speed field, enter a new speed, and press ENTER.
NOTE: If the boat is not moving fast enough or the speed
sensor is not registering a speed, a “Boat Is Not Moving Fast
Enough To Calibrate” message appears at the bottom of the
screen. Check that the speed sensor wheel is moving or safely
increase boat speed. If there is a problem with the speed sensor,
or if a speed senor is not installed, a “Water Speed Sensor Is
Not Working” message appears at the bottom of the screen.
Check the connections of the speed sensor cables.
Graph Sub Tab
The available Graph sub tab options are:
• Fish Symbols—sets how the Sonar Page interprets
suspended targets and background information. If you select
a fish symbol, the GPSMAP 392/398/492/498 identifies
some returns for you by replacing them with fish symbols
(in large, medium, and small sizes based on the size of the
sonar return). If you are using dual beam, fish symbols from
the narrow beam (directly underneath your boat) are solid,
and the returns from the wide beam (out to the sides of your
boat) are hollow.
The Sonar Page does not interpret the sonar return data.
Suspended targets appear as symbols. No background
information appears
Same as previous with the target depth shown.
Suspended targets appear as symbols. Background
information appears, making the distinction between
fish and structure easier.
Same as previous with target depth shown.
