The median flux (blue), polarised flux (red), and normalised q′ and u′ Stokes (green) spectra for 4C 38.41. These spectra were compiled from 144 spectropolarimetric observations of the blazar. The polarised flux spectrum is derived by multiplying the flux spectrum by q′ and displays a featureless power-law as expected from a synchrotron source. The polarised flux spectrum is scaled by a factor of 10 for clarity. See the text for a full description of the q′ and u′ spectra. Telluric absorption features are identified with  ⊕  symbols.