Extinction comparison between the TGE A₀ optimum HEALPix map and the Planck A_V HEALPix level 9 map at small extinction values. The colour scale shows the density of HEALPixes, the red dashed line represents unity, and the points with error bars are the median A₀ and average absolute deviation computed in A_V bins of width 0.025 mag. The red line is the result of a linear fit to the points.