In detector band 3 large fringes are present. These fringes can shift with the position of the source in the slit. A small mispointing (within the specs of ISO) can shift the fringes over 1/4 P. Before measuring line fluxes of unresolved lines in this band, it has to be checked if the fringes in the spd before respcal are in phase with the fringes in the RSRF. If not, the fluxes of unresolved lines in band 3 might be off by 25% since the relative size of the fringes is about 50%. If one removes the fringes in both RSRF and spectrum in the Fourier space before applying respcal, then this problem and the problem of residus of fringes is solved at once. This also means line fluxes measured with fast AOT1 observations that cannot resolve the fringes in band 3 are only reliable for less than 25%.