II Morrow Inc. 920 GPS - Manual (Page 55)

Magnetic Variation
This option allows you to override automatic
magnetic variation and manually enter a
variation value. This is normally not required
for navigation anywhere in the world except
near the poles, where magnetic variation is the
greatest.
If manual entry of magnetic variation is
necessary, obtain the correct value from a
reliable chart or other source. Select “Manual”
and enter the variation value east or west.
To disable magnetic variation, select “True.”
All course headings will show referenced to
true north.
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