Furuno FR-1500 MARK-3 Series User Manual page 34

(a) Echo average OFF
Echo averaging uses scan-to-scan signal correlation technique based on the true motion over the
ground of each target. Thus, small stationary targets such as buoys will be shown while
suppressing random echoes such as sea clutter. True echo average is not however effective for
picking up small targets running at high speeds over the ground.
Echo average is inoperable when a compass signal is not available. If you wish to use this feature
without a compass signal, consult a FURUNO representative.
Do not use the Echo Average function under heavy pitching and rolling; loss of
target detection can result.
(b) Echo average ON
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