In the following figure from the book "rissel h, ruge i, ion impantation"
https://photos.google.com/search/_tra_/photo/AF1QipON1MxI30Cta0f80fq1lqiR4nh0upk2fdakI1lc
https://photos.google.com/search/_tra_/photo/AF1QipMYwKbSJiJGAKHfkXeiGJAI8z4tFn9QZfwNsBoX
which dimension is called "shoulder of the system"