Our position inside the Galaxy requires all-sky surveys as input for Galactic 3D-emission modeling or studies of local synchrotron structures. Interferometric measurements but also single-dish observations miss large-scale structures and need to be complemented in an appropriate way. Absolute calibration is 'a must' for the interpretation of Galactic polarization structures
resulting from Faraday rotation in the interstellar medium. Large-scale polarization calibration measurements are very difficult to do at high frequencies from the ground. However, polarization data from WMAP are at an absolute level and are very helpful to
calibrate ground based polarization observations in the GHz range.