DATUM All of Atlantic Mapping's charts are designed to be used with the 1927 NAD (North American Datum).GPS units have many datums stored within their software and can easily be changed in the settings menu options. Most GPS units purchased today are set to a default setting for WSG84. In order to use the pre-selected coordinates or the GEO Plot System on our charts you will need to change your datum to 1927 NAD. Some GPS units depending on their brand list this as 1927 NAD CONUS. If you do not see 1927 NAD in your list of datums call your GPS unit manufacturer. Once you have your datum selected you now need to choose your Positioning Format. You will have just a few choices in your scroll settings and the one you want looks like the following:
DD MM SS.SThis selection will allow and show 2 digits for degrees, 2 digits for minutes, and 2 digits for seconds a decimal then 1 digit representing a tenth of a second. Every tenth of a second accounts for approximately 8'. Some GPS units only go as far to show DD MM SS; in this case you will need to round off your tenth of a second to the closest second for input purposes.
So to put it all in simple terms, you must set your GPS unit's Datum and Positioning Format to accurately use our charts.