Furuno CSH-7 Operator's Manual page 48

Figure 8-8 Echo-1 test display
Echo-2 test
This test checks echo processing circuits in the display unit and
transceiver unit.
TRX ECHO TEST
PRESS [MENU] 2 or 3 SECONDS TO STOP SELFCHECK
Figure 8-9 Echo-2 test display
Note: Appearance of above test pattern may vary slightly
depending on the frequency or internal settings.
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