The RSRF was intensively measured in the lab. The calibration source used was a cryogenic black-body source with temperatures between 30 and 300K. After the launch of ISO, the recalibration of the RSRF was performed on standard stars and asteroids using a special calibration uplink procedure to make sure that we scan more than the allowed wavelength range for each AOT band. Furthermore this observation mode is much quicker than the standard line scan mode (AOT 6) and each scanner position is scanned.
The RSRFs are derived using the Interactive Analysis package for SWS. The measurements are processed as in the standard pipeline till before the flux conversion steps (till after dark). The RSRF is then obtained by dividing this raw spectrum by a model of the source we observe. This means that for stellar sources with spectral features, small inaccuracies in the model can introduce false features in the RSRF, and thus in every spectrum processed with this RSRF. Therefore, extreme care has to be taken before 'correcting' the RSRF.