Spectro-polarimetry of the non-polarized standard star HD   97689 observed with FORS2 during night 2010-05-04. The measured reduced Stokes P_Q and P_U profiles, both with a value of  ~ 0.1% are indicated in solid blue lines, with the statistical error bars in red. In both panels, the black dotted lines show the total flux (in arbitrary units), and is not corrected for the instrument + telescope transmission functions.