In order to determine the polarization of the recoil protons, the Cherenkov gas detector behind the focal plane of spectrometer A can be replaced by a carbon analyser and a package of two Horizontal Double-Driftchambers.
The polarization measurement is based on the fact, that scattering of polarized protons in carbon shows an asymmetry in the distribution of the azimuthal scattering angle.
The thickness of the carbon analyser can be varied between 1 and 7 cm, depending on the kinetic energy of the incident protons (50-200 MeV).