Redshift-distance relation measured by BAO surveys, compared to the predictions of the ΛCDM model constrained by Planck. The grey band centred at unity shows the ±1 and ±2σ confidence regions for the Planck prediction, given the remaining uncertainties in the parameters. This is a percent-level prediction of the distance scale. The BAO points are: 6dFGS, green star (Beutler et al. 2011); SDSS MGS, purple square (Ross et al. 2015); BOSS DR12, red triangles (Alam et al. 2017); WiggleZ, blue circles (Kazin et al. 2014); SDSS quasars, red circle (Ata et al. 2018); and BOSS Ly α, yellow cross (Bautista et al. 2017).