Top panel: polarization degree as a function of frequency as measured by Planck (black dots), WMAP (blue triangles), XPOL (yellow diamond), POLKA (green cross), and NIKA (red crosses). The NIKA and POLKA values have been estimated by aperture photometry considering the source extension up to 9′. Planck and WMAP values are shown at their native resolution. XPOL, NIKA, and POLKA values have been integrated over the source. The solid line represents the weighted-averaged degree for all experiments but POLKA. Dashed lines represent 1σ uncertainties. Bottom panel: polarization angles in Galactic coordinates for the same five experiments. The solid line represents the weighted-averaged polarization angle computed using all the values.