The accuracy of the area scanning technique depends on observing conditions resulting from seeing, tracking irregularities of the telescope, photon and seeing statistics (integration time and the size of the telescope), and the atmospheric spectral dispersion of the stellar image in the spectral region used. In addition, the reduction method as well as the mechanical and optical quality of the telescope and photometer influence the accuracy of the results.

The tracking error of the telescope is usually larger than the observer believes. The amplitude of the periodic error of the worm gear is at best ± 0.5 arc sec with period length between 4 and 10 minutes, depending on the particular telescope. Figure 1 shows the tracking error for the ESO 50 cm and 100 cm telescopes. Other telescopes usually fit in between this two extremes.