The Torino Photopolarimeter is capable of simultaneous polarimetric measurements in
UBVRI colors, with four dichroic filters splitting the optical paths of the UBVRI
components of white light in such a way as to feed five separate photomultipliers
that measure each color simultaneously.  A half-wave plate in front of a calcite
block splits the incoming radiation into two components with polarization planes
mutually orthogonal to each other.  Rotation of the half-wave plate by steps of 22.5
degrees and corresponding measurements of the intensities of the two rays allow the
observer to derive the values of the Stokes parameters and hence the value of the
degree of linear polarization and the position angle.