Caption: Simulation of how the binary system shown in the previous figure would appear on the detector of an interferometer-spectrograph combination with 20 cm apertures separated by 3 meters (these parameters correspond to the initial configuration for ELFS). The simulation assumes that the separation of the two components of the binary is 5 milli-arcsec, that the observation is taken at maximum separation, and that the point spread function in the dispersion direction is a delta-function (a reasonable approximation of ELFS beam, which is highly compressed in the dispersion direction). The pattern has been normalized to unity at each wavelength for display purposes. The vertical lines indicate the locations of the individual components. Notice how distinct the shift in the centroid as a function of wavelength appears, even though the binary is not resolved at any given wavelength. Because the centroid is dominated by the cool component at the longest wavelengths and the hot component at the shortest ones, the wavelength dependence of the centroid provides an unambiguous measure of the angular separation of such a system.