vish02
Incidence (sadly) means different things to different people, in different circumstances and different times in history.
Many years ago it was commonly used as a measure of what we would today call Angle of Attack. Indeed Dave's use of it on page 120 is (I suspect) in the Angle of Attack sense.
To an engineer (yesterday or today) Incidence is the physical rigging angle of an aerodynamic surface (usually the wing or tailplane) with respect to some datum line.
To a pilot today Angle of Attack is the angle between the chord line of an aerofoil and the direction of the local airflow as it approaches the aerofoil.
Is that any help?
JF