Simrad IS20 Manual page 62

Apparent wind offset
Any residual error in the apparent wind angle display can
be corrected manually by entering the required offset.
A positive value indicates starboard offset angle, a
negative value indicates port offset angle.
Compass
The compass calibration and the heading offset function
affects the compass that is selected as heading source.
If more than one compass is connected to the system,
each compass have to be manually selected as compass
source (sensor) and calibrated separately. Refer to
Manual source selection, page 38.
62 | Configuration
Range
-180 - +180
The calibration procedure will have no effect on earlier
compass models from Simrad and non-Simrad
compasses!
Step Default value
1
Units
0 °