Simrad HS50 - Manual (Page 40)

Simrad HS50 Heading Sensor
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20221081 / F
The average value for observations from each of the two
different systems should then be used, and the offset between
the two systems (reference value minus HS50 reading) input as
the Head offset value.
The offset value can be either positive or negative.
Example:
If the heading measured by the reference system is 32.1° and the
HS50 heading 28.5° during the calibration period, 3.6 (32.1 -
28.5) should be entered in the General submenu as the Head
offset value.