  We show that the outcome of disc instability models is strongly influenced by
boundary conditions such as the position of the inner and outer disc edges. We
discuss other sources of uncertainties, such as the tidal torque, and we
conclude that disc illumination, disk size variations and a proper prescription
for the tidal torque must be included in models if one wishes to extract
meaningful physical information on e.g. viscosity from the comparison of
predicted and observed lightcurves.
