Garmin GPSMAP 178C Owner's Manual page 123

Understanding the Graph
It is important to understand that the unit does not display a 3-D representation of the underwater
environment. The unit can display multiple things at the same time, but cannot determine where the
return originated – only when it was received.
Examples 1 and 2 provide a look at the underwater world from a top view, and illustrate how these
views would be displayed on the graph. On both graphs it appears the fi sh and tree are side by side
as shown in Example 1. However, when we look at Example 2, we see that the fi sh can be several feet
from the tree. It is important to remember that the sonar cannot determine where in the coverage area
the tree or fi sh are, only that the returns were received at the indicated depths in the same time frame.
Enlarged
Transducer
View
Example 1.
Enlarged
Transducer
View
Branches
Fish
Branches
Fish
Example 2.
Appendix G
Understanding the Chart
Remember that the sonar displays a 2-D picture of the
underwater environment. The fi sh and tree could be
located anywhere in the coverage area at that time.
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