Well I really thank you for your help.
I think after looking
or
a few times I will get it
I mean, it is simple geometry, some logic and mathemathics

But at my first time I saw this kind of videos I do understand nothing, and I am out of school for over 10 years
And for sure: i have to do some test-runs to get a feeling for that. Quasi a "d(r)iving-school" ;D