|Δτ| versus separation in parsec between central and off-axis sight lines for absorption lines matched within ±6 km s⁻¹. The horizontal dashed line marks median |Δτ|, and dotted lines represent 1σ scatter based on the median absolute deviation. The median |Δτ| in equal frequency bins with 1σ scatter which are essentially Δτ_rms, are also shown. The 1σ uncertainty on averaged |Δτ| per bin is 0.02 and not shown. The measurements at |b|< 10° are marked as ‘+’. The power law fit to |Δτ| at |b|> 10° is also shown. For clarity, 9 measurements in the range 1.39 < |Δτ| < 2.53 have been omitted from the plot.