  The Sydney University Stellar Interferometer (SUSI) has two beam combiners,
i.e. the Precision Astronomical Visible Observations (PAVO) and the
Microarcsecond University of Sydney Companion Astrometry (MUSCA). The primary
beam combiner, PAVO, can be operated independently and is typically used to
measure properties of binary stars of less than 50 milliarc- sec (mas)
separation and the angular diameters of single stars. On the other hand, MUSCA
was recently installed and must be used in tandem with the for- mer. It is
dedicated for microarcsecond precision narrow-angle astrometry of close binary
stars. The performance evaluation and development of the data reduction
pipeline for the new setup was assisted by an in-house computer simulation tool
developed for this and related purposes. This paper describes the framework of
the simulation tool, simulations carried out to evaluate the performance of
each beam combiner and the expected astrometric precision of the dual beam
combiner setup, both at SUSI and possible future sites.
