Garmin Fishfinder 250 Owner's Manual

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Garmin Fishfinder 250 Owner's Manual Manual pdf 29 page image

21• Heading — select the reference used in calculating heading information for the the followingAdvanced data fields: Bearing, Compass, Course, and Track (see pg. 17-18). ‘True’ will display datawith reference to True North. ‘Magnetic’ will display data with reference to Magnetic North using themagnetic variation value received in the RMC NMEA sentence (see pgs. 5-6).Sonar TabAllows you to set up initial settings and calibrations. The following settings are available:• Water Type — since sound waves travel through ‘Fresh’ and ‘Salt’ water at different rates, it isnecessary to select the ‘Water Type’ to ensure accurate readings on the unit.• Depth Number — controls the efficiency of the digital depth update rate. ‘Fast Sonar Update’updates quicker and is recommended for low-noise, deeper water (>50 ft.). ‘Auto’ is best for shallowwater or high noise areas, has a slower screen update, and is best used if you travel a wide variety ofdepths. If the unit is unable to track the bottom for any reason, the digits in the depth window flashon and off to alert you.• Automatic Scroll Speed Limit — automatically adjusts the Scroll rate (see pg. 14) to the speedof your vessel (if equipped with a speed sensor or receiving GPS NMEA input). Entering your maximumcruising speed will produce a 100% scroll rate when you reach that speed. One half of that speedwill produce a 50% scroll rate, etc.• Keel Offset — allows you to offset the surface reading for the depth of a keel in order to measuredepth from the bottom of your keel instead of from the transducer’s location. Enter a positivenumber to offset for a keel. It is also possible to enter a negative number to compensate for a largevessel that may draw several feet of water. The ‘Keel Offset’ will be reflected in the depth reading.• Transducer Type — does not appear in Simulator Mode. Allows you to specify what type of trans-ducer you are using. ‘User Defined’ is reserved for future use. Do not use unless instructed.• Calibrate Water Speed — this will only appear if you are using a speed-capable transducer/sensor.Calibration is required to ensure that the Water Speed displayed on your unit is accurate. The unitautomatically uses GPS ground speed (if available via NMEA input) for comparison on the calibra-tion. If a GPS ground speed is not available, use either your boat’s speedometer reading (not alwaysUnit OperationMain Menu OptionsTransducer at SurfaceEnter (+) positive Keel Offsetnumber to show depthfrom bottom of keelTransducer at Bottom of KeelEnter (-) negative Keel Offset number toshow depth from surfaceMain Menu - Sonar Tab