Expected interferometric signal corresponding to the configuration of the system of υ Sgr during the 2008 interferometric observations applying the parameters from (Koubský et al. 2006; Netolický et al. 2009). Upper panel: the flux ratio of the component is 10. Lower panel: the flux ratio of the component is 100. The solid line represents the S1S2 short baseline and the dashed line the W1W2 long baseline. The vertical lines define the spectral bandpass used for the V² measurements described in Sect. 2.1.2. The measurements are shown as crosses with error bars (S1S2 measurements) and diamonds (W1W2 measurements).