I had a different lamp model in mind then the on proposed by Michael. It is a very standard desk lamp but, the problem is that it has 2 “hinges” per joint.
I found how to link a bone to another as “child of”. With that, I can incline both bones of the arm as one !
But when I incline my arm and then rotate my stem bone, things get all wacky.
I am going to complete the lesson with Michael’s design then come back to this attempt later.