RT_INS_Heading_Gradient: INS Heading and Gradient
RT_INS_Heading_Gradient: 142, 20 (0x8E1420 + unit id) (0x394)
Byte 0: Validity
Byte 1: Accuracy heading
Bytes 2-3: INS heading (degrees in the range -180 to 180)
Byte 4: Accuracy gradient
Bytes 5-7: INS gradient (degrees)
Resolution of heading and gradient is degrees/100.