In order to derive physical parameters from the data in an observation, the SAS uses the RGS instrument model encapsulated in the calibration data stored in the CCF. These data are not supplied with the ODF or PPS products but are available for immediate download [28], along with procedures to ensure your calibration data remain up-to-date and the latest instrument news [29]. The CCF is an accumulation of all the calibration data ever released so that one of the initial SAS tasks is to use the task cifbuild to build a calibration index file ccf.cif that enumerates which CCF components apply to an observation. A more complete discussion of these matters appears elsewhere in this manual in § 2.3.3 and § 3.11.