Trimble Outdoors SPSX51 - Manual (Page 126)

A NMEA-0183 Output
124 SPSx51 Modular GPS Receivers User Guide
HDT Heading from True North
The HDT string is shown below, and Table A.5 describes the message fields.
$GPHDT,123.456,T*00
Table A.5 Heading from true north fields
Field Meaning
0 Message ID $GPHDT
1 Heading in degrees
2 T: Indicates heading relative to True North
3 The checksum data, always begins with *