RT_GPS_Heading_Gradient2 Heading and gradient 2
RT_GPS_Heading_Gradient: 140, 21 (0x8C1620 + unit id) (0x316)
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Byte 0: Validity
Byte 1: Accuracy Heading
Bytes 2-3: GPS Heading (0-360 degrees)
Byte 4: Accuracy Gradient
Bytes 5-7: GPS Gradient
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Resolution of heading and gradient is degrees/100