Interferometer (scalar averaged cross-power amplitude over the full duration of the observation) spectra of the H₂O masers toward NML Cyg obtained with the inner 5 antennae of the VLBA at five epochs. The vertical dash-doted line indicates the maser feature at V_LSR of 5.22 km s^-1 which served as the phase-reference. The lower panel shows a 100-times blow-up of the H₂O spectra shown in upper panel. (This figure is available in color in electronic form.)