To obtain more reliable orbital solutions, we went through a strict pro- cess of astrometry selection and remeasurement. First, we selected the few astrometric observations obtained by professional surveys: Pan-STARRS 1, Kitt Peak, and Siding Spring Survey. It is worth pointing out that most of the time C/2013 A1 was at high negative declination, and therefore was not observable from the Northern Hemisphere where most professional surveys are located. Then, we added observations that we obtained at the Mauna Kea and Cerro Paranal observatories. Finally, to obtain a good time coverage and increase the number of ob- servations we asked other observers to provide us with their images so that we could remeasure the astrometric positions prior to the encounter. We obtained and remeasured more than 200 images obtained at the following observatories: • Swift space telescope (this was first time Swift has been used to obtain small body astrometry); • RAS Observatory, Moorook; • Sutherland-LCOGT A and B; • iTelescope Observatory, Siding Spring; • Siding Spring-LCOGT A; • Blue Mountains Observatory, Leura; 9