  For the astronomical community analyzing ISO-SWS data, a first point to
assess when judging and qualifying the observational data concerns the flux
calibration accuracy. Since the calibration process is not straightforward and
since a wrong calibration may lead to an over- or underestimation of the
results, knowledge on the full calibration process and on the still remaining
calibration problems is crucial when processing the data.
  One way to detect calibration problems is by comparing observed data with
theoretical predictions of a whole sample of calibration sources. By using an
iterative process in which improvements on both the calibration and the
theoretical modelling are involved, we will demonstrate that a consistent
theoretical data-set of infrared spectra has been constructed. This data-set
has been used to derive the OLP10 flux calibration of the ISO-SWS. We will
shown that the relative flux calibration accuracy of (high-flux) ISO-SWS
observations has reached a 2% level of accuracy in band 1 and that the flux
calibration accuracy in band 2 has improved significantly with the introduction
of the memory-effect corrrection and the use of our synthetic spectra for the
flux calibration derivation, reaching a 6% level of accuracy in band 2.
