Raymarine GPM400 Reference Manual page 109

Manual Scroll Speed
Specify the speed at which the fishfinder view updates and scrolls.
Select Transducer
When selecting a transducer, the DSM reports to the G-Series
whether it sees a 600W or 2kW transducer. This allows you to
select an appropriate transducer from the list.
Select Speed Transducer
This option is only available if the selected transducer is one that
does not include an integrated speed transducer.
Frequency Calibration
Hides the setup menu and brings up a set of soft keys to tune the
transducer frequencies.
Depth Offset (waterline)
Offset represents the depth of the transducer (relative to the
waterline)
Speed and temperature offsets
Calibrate the speed transducer and thermistor (if fitted).
DSM Reset
Restores all settings to factory default.
Trip Counter Reset
Zero the trip counter.
Interference Rejection
Removes spikes caused by interference from other fishfinder-
enabled vessels.
2nd Echo Interference Rejection
Finely adjust the ping rate according to the 2nd echo level.
Ping Rate Limit (per sec)
Provides a speed limiter. It can be useful to adjust ping rate to suit
local conditions, for example when you are over a hard seabed or
in shallow water.
Ping Enable
Normally enabled, you can disable the ping when appropriate: to
test other equipment, or if there is a diver beneath the vessel, for
example.
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Chapter 8: The Fishfinder