Projection of the hand model active workspace in the plane orthogonal on the pronation-supination motion axis when the assembly palm-fingers is stiffened. This complex surface covers the spaces described by the fingertips in pronation-supination motion (only joint 2 is moving). During this motion the thumb is always placed in 3D regions with coordinate z < 0. The fingers' tips trajectories are circle arcs situated in various planes parallels with y
0. In the point whose coordinates are y = 0 z = 0, the middle finger is always pointed, because the rotation axis is even its static position. At 4 cm far from this point the circle described by the thumb is placed. At 2 cm from the origin, there are placed, symmetrically with respect to O
0, the trajectories of index and ring finger. The pinkie's trajectory is the circle with radius of 3.3 cm.