Departure of the P_r of 67P dust in each apparition from to the average trend. The black fitting line in Fig. 6 now corresponds to the horizontal dashed lines at ΔP_r = 0. The horizontal solid lines and shaded areas denote the weighted mean and error, in which the colour scheme follows the symbols in the legend. Open and filled symbols denote the pre- and post-perihelion data of 67P dust. Only post-perihelion data were used to estimate ΔP_r.