I guess “airplane is a cantilever” helps more to understand. The airplane drawing resembles cantilever for me.
That's how I see it, assuming the stylus is at the centre of the aeroplane in that graphic at the intersection of the three parameters.
It is not the cantilever that is skewed but the stylus itself on the position and the way it is mounted onto the cantilever.
Sure - I can think of cantilever in the picture as well. no problemo.
For quite a while now when doing an alignment we aligned on the cantilever. I keep coming back to the Uni-PRO or the SmartTractor tools and instructions with its mirrored surface. We can see enough of the stylus to get it to the correct effective length distance, the divot in the tool, and then adjust the zenith of the cantilever according to the marked lines. But we can't see the stylus so well to align its zenith. So thinking of the diagram in terms of the cantilever works.
My understanding of the 'zenith error' discussed by WallyTools is about the stylus as mounted on the cantilever as shown in the 'final Frontier' link that Bonesy posted. This takes alignment down to the stylus level so I applied the terminology to it. Of course the cantilever can use the same terminology as it holds the stylus.
As long as we use the terminology to denote what we're talking, its all good.