Heading displayed in degrees



My 1622 displays heading/course in True, can I change it to Magnetic?
I've got it connected to a Garmin 198C Sounder that displays Magnetic with automatic variation from True. Do I have something wired wrong to the 1622?
These are the NMEA0183 sentences that the 1622 accepts:
Interface (NMEA 0183 format) – –: any talker
$– –BWC, $– –BWR, $– –DBK, $– –DBS, $– –DBT,
$– –DPT, $– –GGA, $– –GLC, $– –GLL, $– –GTD,
$– –HDG, $– –HDM, $– –HDT, $– –MTW, $– –RMA,
$– –RMB, $– –RMC, $– –VTG
The displayed information is dependent on the output of the NMEA talker which may or may not be the same as what is displayed on your Garmin. The conversion to magnetic on your 198 display may not be the same as what is transmitted in the NMEA data.