• CAO, San Pedro de Atacama; • Murrumbateman. For these stations, we performed the astrometry with track and stack pro- cedures, and corrected the astrometric positions by as much as 2 $^{′′}$. For each image, we estimated the astrometric error from the image quality, following a scale that assigned 1 pixel astrometric error to all the images where an obvious star-like central condensation was visible, and 2 pixels to more prob- lematic cases where the central condensation was either diffuse or blurred (due to poor seeing conditions and/or tracking). We evaluated a few in- termediate cases at 1.5 pixels. We set the data weights by conservatively applying a scale factor 2 to the estimated uncertainties. Figure 2 shows the right ascension (RA) and declination (DEC) 2 residu- als against solution 102, which is our current best estimate for the comet’s trajectory and is described in Sec. 3.4. It is clear how important the remea- surement and observation selection process was: the selected and remeasured astrometric observations have smaller errors than the excluded data. In par- ticular, some of the observations we filtered out during our selection process have residuals as large as 5 $^{′′}$, while the astrometric positions replaced by our remeasurements have residuals as large as 2 $^{′′}$. $^{2}$In this paper RA and DEC are always referred to the equatorial J2000 reference frame. 10