Left: distribution of the optical centre offsets relative to their Planck SZ positions for the validated clusters (Flag=1–3) presented in Table A.1. The inner dashed line corresponds to a radius region, which encloses 68% of the PSZ2 confirmed clusters. The external dotted line encloses 95% of clusters and corresponds to 6′. Cases with multiple optical counterparts have been excluded from this analysis. Right: cluster optical centre offsets relative to their Planck SZ position as a function of cluster redshift for a sample of 50 sources. The dashed horizontal line is 5′, which represents the maximum offset expected for a Planck SZ detection (i.e. FWHM Planck multi-frequency combined beam). The dotted line corresponds to the physical 1 Mpc radius region at the corresponding redshift.