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Using the Sonar Page
When combined with a GSD 21 Sounder Module, your GPSMAP
378/478 becomes a powerful shnder/asher with the Sonar Page.
If a GSD 21 is attached, but the unit does not detect a transducer,
a “Sonar Turned Off” message appears across the Sonar Page. The
Sonar Page appears only if a GSD 21 has ever been attached or
when the unit is in Simulator Mode.
The middle of the page contains a right-to-left moving sonar image
of the water beneath your boat. Items appear as they pass under your
transducer. Those items on the right side of the screen are closer to
you than those on the left. Along the right side of the screen is an
adjustable scale that reects the depth of the area being shown. The
top left corner shows the adjustment option, the depth, and the water
temperature.
Sonar Page
The sonar returns show as red (strongest), then orange (strong),
yellow (medium), green (weaker), and blue (weakest). The Fish
Symbols option allows you to view the actual sonar data, a sh
symbol or a combination of both. When the unit is set to Dual, the
appearance of the sh symbols changes. Fish symbols from the
center of the beam (200 kHz) are solid (or narrow arches), but the
returns from the edges of the beam (50 kHz) are hollow (or wide
arches).
The sonar display can also be set to show a split screen view of a
zoomed portion of the sonar, bottom lock (display scaled from the
bottom up), or a combination of these options. For example, you
can choose to show dual frequency at a 2X zoom (Dual 2X) on one
half and normal range dual frequency (Dual) on the other half. The
current display mode appears at the bottom of each sonar display.
Read the “Understanding Sonar” section beginning on page 112 for
more on information about sonar.
104 GPSMAP 378/478 Owner’s Manual
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