Left: proper motions of 6.7 GHz methanol maser cloudlets in G23.657–00.127 as measured relative to the centre of motion. The centre of motion, defined in Sect. 2, is marked by the plus sign. Its relative coordinates to the brightest spot in E1, as given in Table 1, are (−31.6145 mas, −88.7120 mas). The cloudlets are marked by filled circles, their sizes are proportional to the peak brightness at the first epoch. Their colours correspond to the local standard velocity scale presented in the vertical wedge. The black arrows indicate the best fits of the relative proper-motion for the three epoch data with the uncertainties marked by the grey triangles. The dotted ellipse traces the best flux-weighted fit to all cloudlets (except the SW blue-shifted one) as detected at E1. The centre of the ellipse is marked by the cross (Table 2). Right: proper motions estimated via ellipse fittings and aligning their centres. The (0,0) point, marked by the plus sign, corresponds to the centre of the best fitted ellipse to E1 (Table 2). The black arrows represent the averaged proper motion vectors, defined as in Sect. 2, between E1–E2 and E1–E3 data.