PZPO for the QSO sample with G > 17 mag as a function of sin β. Black open circles represent the observed data (the weighted mean) to be compared to the blue open circles that represent the L20 correction (the unweighted mean as the L20 correction carries no error). The black filled circles represent the corrected parallax data (according to Eq. (5)) to be compared to the red filled circles that represent the spatial correction at G = 20 mag at HEALPix level 2 (both are weighted means, but the error in the red filled circles is too small to be visible).