Relative position accuracy between epochs checked on stars after the final registration (panels ΔX and ΔY) and flux matching accuracy checked after seeing and flux matching (lower panels). The ΔX and ΔY values are the offsets in X and Y (in pixels) between the measured epoch and the reference epoch (i.e. epoch 4). Epoch 1 is shown to the left, epoch 2 in the centre, and epoch 3 to the right, all plotted with respect to reference X-pixel. In the lower panels we show the flux ratio for the same stars. Black dots indicate all stars, red crosses show stars rejected due to large FWHM and/or high flux ratio, and blue circles indicate stars used for the accuracy calculations.