Hi,
I’ve followed the video instructions + set the bone armature shape to sticks for a better visibility.
Here is the result:
I snapped the tail of the “Stem” bone to the middle of the arm axis thanks to Shift+S.
I have also constrained the movement of “Arm A” bone to rotate only along the X axis, but I guess Lecture 114: “Constraining Bones movement” will talk about that, so I will see if I have done right
Cheers !