GPCC application to 3C120. Top: posterior distribution of delay with prior p(τ) = 𝓊(0, τ_max(l, Z)). The peak with the highest probability corresponds to a delay of 27.6 days. Middle: posterior distribution of delay with flat prior p(τ) ∝ 1. Bottom: ICCF calculated with a sampling of 1 day for linear interpolation of fluxes. The centroid is determined using the 80% rule. Our results for the ICCF peak and centroid are identical to those of G+2012, and we show the results of G+2012 including the uncertainty estimated with the FR/RSS method. All delays are indicated in the rest frame.