GARMIN RECEIVERS AND THE NMEA DATUM PROBLEM
              Rev. 21 Feb. 2002

Garmin does not use a standard NMEA when it comes to datums...  
The NMEA should always be WGS-84, but Garmin sets it to the 
datum you select in the GPS...  But Ozi has the facilities
to correct this...

Considering you have a DRG map (with an NAD-27 datum) 
displayed by Ozi:

1. Set your GPS to NAD-27 CONUS datum...

2. For up/downloading stored data (waypoints and tracklogs 
   (in the GRMN mode) Garmin outputs them all in WGS-84, so 
   leave Configuration > GPS > "GPS Upload/Downlod Datum" 
   to WGS-84 no matter what the map datum is...  Ozi will 
   correct for this because you (or the map itself) have 
   told Ozi that it's an NAD-27 CONUS datum map...

3. For real-time tracks (NMEA mode) you must set Configuration > GPS 
   > NMEA Output Datum -to NAD-27 CONUS, because the tracks and 
   waypoints coming out of unit are in the datum that the 
   unit is set to...  This is necessary to prevent the map program
   from also correcting the NMEA data which isn't necessary and
   would cause a "double correction" error...

Now the up/downloaded waypoint coordinates shown by the GPS and Ozi 
will be exactly the same...

Also the real-time NMEA current positions shown by the GPS and that 
shown by Ozi (down at the bottom) will be exactly the same...

Jack Yeazel