Luke Skywalker writes:

Well not remembering which jet leaves the field wide open...but if it
was on the pedestal of a B737 200 series or a B727 or a B707 you were
looking at the rudder trim knob.

I thought of that, but this was larger ... and you wouldn't normally use
rudder trim to turn the aircraft.

I guess it could be a manual turn controller for the autopilot, as Bob said,
but I wonder how it was used and why it's gone now. Maybe it was something
like control wheel steering (also apparently not used much in practice).

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