19• Heading — lets you select the reference used in calculating heading information for the the Bearing,Compass, Course, and Track Advanced Data fields (pg. 14). ‘True’ will display data with reference toTrue North. ‘Magnetic’ will display data with reference to Magnetic North using the magnetic varia-tion value received in the RMC NMEA sentence (see pgs. 3-4).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’ willupdate quicker and is recommended for low-noise, deeper water (>50 ft.). ‘Auto’ is best for shallowwater or high noise areas, will have a slower screen update, and is best used if you travel a widevariety of depths.If the unit is unable to track the bottom for any reason, the digits in the depth window willfl ash on and off to alert you that the unit is not tracking the bottom.• Automatic Scroll Speed Limit — automatically adjusts the Scroll rate (see pg. 12) 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. This makes it possibleto measure depth from the bottom of your keel instead of from the transducer’s location. Enter apositive number to offset for a keel. It is also possible to enter a negative number to compensate for alarge vessel that may draw several feet of water. The ‘Keel Offset’ will be reflected in the depth read-ing.• Transducer Type — this will not appear when in Simulator Mode. Allows you to specify what type oftransducer you are using. ‘User Defined’ is for future use and should not be used 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 will be accurate. The,Unit OperationMain Menu OptionsTransducer at SurfaceEnter (+) positivenumber to show depthfrom bottom of keelTransducer at Bottom of KeelEnter (-) negative number to show depthfrom surfaceMain Menu - Sonar Tab