TWGOAT,
Here is how I would go about guesstimating the net rotation. But mostly, this is a demonstration of conceptual methodology rather than an exercise in mm or degree 'exactitude'.
I increased size of your ceph so that from the root of your nose to the base of it measured 60 mm on my screen (which is the average length of a nose). Although it might not be your exact nose length, I'm just showing how I would make a ballpark estimate of the net CCW. Also, 'round' numbers are just easier for me to deal with when I'm holding a transparent ruler and protractor up to the screen.
From there, I got a measure of about 50 mm of ANS-PNS (maxilla area) and marked a CUT OUT figure in red where the right side of the figure was about 5mm and left side about 3mm.
It's basically the SEGMENT being removed across the length of the maxilla.
Since the red figure is one where there is more vertical length to the right of it than the left of it, I knew I could draw 2 white lines bordering it and extrapolate them all the way back UNTIL they CONVERGED. I got about 3 degrees. Although subtracting 3mm from 5mm=2mm, the angle measure can differ.
So, the net CCW would be the bottom white line rotating about 3 degrees CCW to meet the top white line. That's the impaction.
Now, if you wanted to do it using the EXACT length of ANS-PNS, you could. I'm just showing the basic METHOD I would use from a geometric perspective.
Illustration included in this post.