S1S2 34m baseline differential visibilities and phases of υ Sgr through the Hα line in August 2008 at Φ_orb = 0.06 (left) and on 27th of July 2009 Φ_orb = 0.65 (right). The 2008 data recorded in five day intervals with similar projected baselines agree well within error bars (dotted lines). The bin size is 0.8 nm in 2008 and in 2009 (4 h 25 baseline: dashed line; 7 h 24 baseline: dash-dotted line). Note the opposite direction of the phase signal between the two epochs.