Comparison of the Type 1 Planck CO maps with the FIRAS J = 1 → 0 (top), J = 2 → 1 (middle) and J = 3 → 2 (bottom) data. The solid orange and dashed blue lines represent perfect correlation (y = x) and the best linear fit, respectively. The best-fit slopes and intercepts are: a) 0.98 ± 0.17 and 0.33 ± 0.65; b) 1.12 ± 0.02 and − 0.01 ± 0.04; and c) 1.13 ± 0.03 and 0.04 ± 0.02.