According NMEA0183 Documentation you swapped the position of Variation field with Deviation field!
HDG - Heading - Deviation & Variation
1 2 3 4 5 6
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$--HDG,x.x,x.x,a,x.x,a*hh
Field Number:
1) Magnetic Sensor heading in degrees
2) Magnetic Deviation, degrees
3) Magnetic Deviation direction, E = Easterly, W = Westerly
4) Magnetic Variation degrees
5) Magnetic Variation direction, E = Easterly, W = Westerly
6) Checksum
According NMEA0183 Documentation you swapped the position of Variation field with Deviation field!
HDG - Heading - Deviation & Variation
$--HDG,x.x,x.x,a,x.x,a*hh
Field Number: 1) Magnetic Sensor heading in degrees 2) Magnetic Deviation, degrees 3) Magnetic Deviation direction, E = Easterly, W = Westerly 4) Magnetic Variation degrees 5) Magnetic Variation direction, E = Easterly, W = Westerly 6) Checksum