Averages and precisions (σ) of the gap in the horizontal and vertical directions as a function of time, when CCD#2 is taken as reference. We note that the gaps of 2016 are based on measurements with the DES r filter and the gaps of 2017 are based on measurements with the SDSS g filter. The black points represent the results derived from the proposed method in this paper, and the red points represent the results derived from the AK03 method. The shaded bars indicate a ±σ x 15 (for clarity) interval around the mean gap location. The values of σ are shown in the panel.