Schematic view of a single beam interferometer. The light paths are represented by light rays. The real light rays are reflected by mirrors up to the beam combiner inside the interferometric lab. However, in this simplified representation, all the mirrors are removed. Thus, the represented virtual light rays are straight lines from the star to the virtual images of the beam combiner. The mechanical structure of the interferometer is reduced to two pivot points, L₁ and L₂ which are the pivot points of the telescopes. The wide angle baseline (WAB) is represented as a vector between the two pivot points: . The OPD measurement is made between the beam combiners and the metrology end point. It is related to the stellar position through Eq. (8).