It allows the rotation of the waterfall target and the solid target ladder around the central axis of the scattering chamber and the vertical translation in order to change the target along the beam line. This is done by a mechanical system schematically shown in fig. 2.3.3.1, and which consists of step motors and absolute optical encoders whose precision is 0.1 mm and 0.1 degree. (see the detailed description in the Appendix A)