GPSMAP 3205 Owner’s ManualusIng sonar > sonar tabGeneral Sub TabUse the General sub tab to select the water type, depth number, automatic scrollspeed limit, scale, keel offset, and transducer type. The available General sub taboptions are:• Auto Gain—controls the aggressiveness of the Auto Gain when the Gainoption is set to Auto. The higher the setting, the greater the number oftargets appear on the screen. The lower the setting, the less clutter on thescreen. The settings are low, Medium (default), and high.• Auto Color Gain—controls what colors are applied to the objects on thescreen when the Color Gain option is set to Auto. Color DCG™ is basedon depth and makes it easier to spot subtle changes in bottom conditionsor fish sizes. DynaColor™ (default) represents the latest in sonar datapresentation and is recommended for all applications. The presentation isbased on bottom strength. It makes the bottom and the fish easier to see andrequires fewer adjustments.• Automatic Scroll Speed limit—automatically adjusts the Scroll rate withthe speed of your vessel. Entering your maximum cruising speed producesa 100% scroll rate when you reach that speed. One half of that speedproduces a 50% scroll rate, and so on. The default is 30.0 kt.• Keel Offset—allows you to offset the surface reading for the depth of akeel. This makes it possible to measure depth from the bottom of your keelinstead of from a transducer’s location near the water line. Enter a positivenumber to offset for a keel. You can also enter a negative number tocompensate for a large vessel that may draw several feet of water, requiringthe transducer to be submerged if you want to measure from the water line.The Keel Offset is reflected in the depth reading.Transducer at surfaceEnter (+) a postvenumber to show depthfrom bottom of keel.Transducer at bottom of keelEnter (-) a negatve number toshow depth from surface.• Transducer Type—allows you to specify what type of transducer you areusing, either Dual Beam or Dual Frequency.• Calibrate Water Speed—this is available only if you are using a speed-capable transducer/sensor. Calibration is required to ensure that the WaterSpeed shown on your unit is accurate. The unit automatically uses the GPSground speed, if it is available, for comparison on the calibration. If a GPSground speed is not available, use either your boat’s speedometer reading(not always accurate) or a stopwatch to determine your speed over a certaindistance (distance / time = speed). It is recommended that the calibrationtake place in water having little or no current.