  An investigation of the stability of the transfer function of the European
Southern Observatory's Very Large Telescope Interferometer has been carried out
through observations of Fomalhaut over a wide range in hour angle. No
significant variation in the transfer function was found for the zenith angle
range 5-70 degrees. The projected baseline varied between 139.7 m and 49.8 m
during the observations and, as an integral part of the determination of the
transfer function, a new accurate limb-darkened angular diameter for Fomalhaut
has been established. This has led to improved values for the emergent flux,
effective temperature, radius and luminosity.
