Ugo: "Coupling is the fact that we can't control ffj1 and ffj2 independently (same applies to middle, ring and little j1 and j2). They are physically linked together, we can only send one target to joint 0 (which is the sum of j1 and j2). Then the joint 1 and joint 2 are going to some ratio of the global target. (in some versions of the hand, this ratio can be fixed, with a bit of magic from Matthew)."
Ugo: "Coupling is the fact that we can't control ffj1 and ffj2 independently (same applies to middle, ring and little j1 and j2). They are physically linked together, we can only send one target to joint 0 (which is the sum of j1 and j2). Then the joint 1 and joint 2 are going to some ratio of the global target. (in some versions of the hand, this ratio can be fixed, with a bit of magic from Matthew)."