Avidyne IFD540 Pilot's Manual page 165

In OBS FROM (defined as the difference between the selected
OBS course and the aircraft course to the fix is  90), the
system will activate the reciprocal course away from the station
with guidance away FROM the fix. The previously active TO leg
will change to white and remain in pivot. The assumption here is
that you will want to fly the leg on the 180 plane between the
aircraft and the fix. If the TO leg is within this plane, you will fly to
the station. If you swing the TO leg to the opposite plane, the
FROM leg would now be in the 180 plane between you and the
fix, and that is the leg to fly – away from the station
OBS FROM Depiction
TIPS AND TECHNIQUES
OBS "Final"
OBS mode can be used to create a user-defined
course into a waypoint/fix or an airfield. Once in
OBS mode, use the external course knob to set the
desired inbound course to the fix or airfield. All
guidance, including that sent to an autopilot, will
now be with respect to that user-defined course.
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