Gaussian fittings of the parallax difference distribution Δω/σ_ϖ, tot for the three G magnitude categories. The distributions were normalised by the quadratically summed errors of the VLBI error with either: the DR3 parallax standard error without any correction (, red line), or with the astrometric excess noise (, blue line), or with the DR3 parallax standard error inflated by the EIF listed in Table 2 and the parallax corrected for the ZPO (, black line representing a standard Gaussian). The dashed lines correspond to the respective standard deviations of the Gaussians, while the solid straight lines show the mean values. The offset of the mean value with respect to 0 is a measure of the ZPO.