Depth    Finders Jones Trolling Motor Services      jonestrollingmotor@cableone.net     870 773 3474 click logo for more information Trying to navigate through the different terminalogy used today on depth finders can be a real challenge.  You have acrynomns such as SI, DI, GPS, CHIRP and others.  Both Humminbird and Lowrance offer depth finders that give this information.  Knowing what each company calls them will help you to determine the unit you need.  Below is a tutorial that may help. SONAR:  Uses a 83 or 200khz transducer to give readings.  These readings show on the screen as colored arches and lines. The colors represent the hardness or density of the object that is relecting the signal. CHIRP:  This is a way the unit (unless you’re using a CHIRP transducer interprets the SONAR signal.  The unit determines the best frequency range for a clearer signal. SI (Side Imaging):  This is self explanatory in that it is for seeing to each side of the boat.  Also known as structure scan, it reveals a picture like image and uses the frequency range of 455 / 800khz. Hummingbird recently introduced a 1200khz or 1.2 Mghz, known as “Mega” to give even clearer detal. DI (Down Imaging): same as SI above, except the readings under the boat. GPS:  A method that is most time overlayed on maps to determine the position of an object.  Using satelites for triangulation, GPS is also capable of determining time, distance, and speed over the water. MAPPING:  Most units come with a mapping software built in, however if you want to see more detail, you would want to consider mapping cards by Navionics, LakeMaster, etc. SIZES:  Units come in a range of sizes and features.  The size is represented by screen measured diagonally.  Obviously, the larger the screen, the more detail can be seen, especially when in a spit screen mode.