Top: mean apparent displacement of C7 as a function of azimuthal angle. Mean and median apparent displacements (full line and dotted lines, respectively) are calculated for angular beam of 60° with step of 30°. Total standard errors of the mean displacement and median displacement (Eq. (1)) are presented. For illustrative purposes, the median curve is shifted to the left by 5°. Bottom: number of apparent displacement vectors of C7 against azimuthal angle. Azimuthal angle counts from the jet axis in direction downstream the jet in anti-clockwise direction. Square roots of the number counts are presented as a proxy for 1σ error. Azimuthal angles of the jet direction are marked by vertical dashed lines at 0° and 180°, while the vertical dot-dashed lines represent the directions transverse to the jet axis, 90° and 270°.