Astrometry of WISE1810. Top: observed relative astrometry of WISE1810 (see legend for the different instruments employed in our study). The GPS data (the oldest images) act as the reference epoch. The best solution including proper motion and trigonometric parallax is shown with a black, solid line. The crosses plotted on the best solution indicate the predicted position of WISE1810 for each observing epoch. Bottom: relative astrometry (right ascension) after removing the proper motion from the data is folded in phase with the 1 yr period (top subpanel). The amplitude of the variation is the trigonometric parallax. The best parallax solution is shown with the black, solid line and the 1-, 2-, and 3σ uncertainty is plotted as a gray-shaded area of decreasing intensity (darkest for the 1σ). The bottom subpanel illustrates the observed minus computed right ascension residuals.