NMEA HDM datagram format
The NMEA HDM datagram provides vessel heading in degrees magnetic. The datagram is no longer recommended for use in new designs. It is often replaced by the NMEA HDG telegram.
Format
$--HDM,x.x,M*hh<CR><LF>
Description
1 $—: Talker identifier
2 HDM: Datagram identifier
3 x.x,M: (Degrees Magnetic
4 *hh: Checksum
Related topics
NMEA datagram formats
I/O Datagram formats