Light curve of a transit event of WASP-11/HAT-P-10 b observed simultaneously with the CA 1.23 m (red points) and the IAC 80 cm (empty orange circles) telescopes. The data of the two telescopes are superimposed to highlight the difference in the light-curve shape caused by the different filter adopted (Knutson et al. 2007). The dashed vertical line represents the time of transit mid-point that, thanks to the two-site strategy, was very accurately measured.