RT_GPS_Heading_Gradient1 Heading and gradient 1
RT_GPS_Heading_Gradient: 140, 21 (0x8C1520 + unit id) (0x315)
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Byte 0: Validity
Byte 1: Accuracy Heading (degrees)
Bytes 2-3: GPS Heading (-180 – 180 degrees)
Byte 4: Accuracy Gradient (degrees)
Bytes 5-7: GPS Gradient
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Resolution of accuracy is degrees/10
Resolution of heading and gradient is degrees/100