PHT-S exhibits a steep beam profile in particular in the cross-dispersion
(spacecraft y-axis) direction, see Section4.5.1.3. As a
consequence, a small pointing offset can cause both a significant absolute
flux offset and a change of the relative spectral shape. The latter is also
visible via flux jumps at the wavelength borders of the order sorting
filters. These borders are situated at 3.7
m for the PHT-SS array
and 8.8m for the PHT-SL array.
Caveat: The accuracies for PHT-S point source spectrophotometry
are only valid for sources within 
3arcsec of the centre of
the aperture. Off-pointings can lead to significant flux losses and
modifications of the spectral shape. Conspicuous artifacts are flux
jumps at the wavelengths of the order sorting filter transitions
at 3.7m for the SS array and 8.8m for the SL array.
It is therefore advisable to cross-check the PHT-S pointing with independent determinations of the source position.