Sensitivity test of the telescope model at a wavelength of 614.9 nm. Top three rows: change in I → QUV for a variation of the mirror retardance τ (left column) and the ratio of reflectivities X (right column). Observations are given by black plus symbols, while the red plus symbols correspond to the 2010 parameter set. τ and X were varied from −10 to 10 and −0.1 to 0.1, respectively. The resulting curves are indicated by the series of blue to purple plus symbols. Bottom two rows: change in V → QU for a variation of the mirror retardance τ (left column) and the ratio of reflectivities X (right column).