A quick example on what $GPXTE messages are. Keep in mind that the sentence Identifier can also be displayed as $GNXTE. The message is the same but some GNSS receivers use this format.
Cross Track Error, Measured
A General warning flag V = warning (Loran-C Blink or SNR warning) A Not used for GPS (Loran-C cycle lock flag) 0.67 cross track error distance L Steer left to correct error (or R for right) N Distance units - Nautical miles
1 2 3 4 5 6
1 A validity 2 A cycle lock 3 4.07 distance off track 4 L steer left (L/R) 5 N distance units 6 *6D checksum