As an example, in the ESO case the exposure type is stored in the ESO hierarchical FITS keyword `HIERARCH ESO GEN EXPO TYPE'. The ESO-MIDAS FITS reader converts that keyword into the MIDAS descriptor _EGE_TYPE. Among the valid exposure types are (according the ESO Archive document): bias, ff, ff-dome, ff-screen, ff-sky, dk, sci. Therefore, when the CCD context is started or after executing the command INIT/CCD links are created between the frame descriptors and the corresponding CCD keyword. With these links the CCD package knows which exposure types are used and which frame descriptor contains the exposure type.
To fill the CCD keywords with these descriptor names a separate procedure is used: eso_descr.prg. A copy of this procedure is put in your working directory. If you need to change one or more descriptor names (e.g. the descriptor name of the exposure time), make the modification(s) and run the modified procedure, using @@ eso_descr.
The CCD package has been developed to reduce CCD data coming from ESO's telescopes on La Silla. However, some flexibility has been built-in to enable the reduction of data coming from non-ESO telescope/instrument combinations, cases in which the telescope and instrument parameters are different. To fill the CCD keywords with the telescope and instrument setup parameters, like name of the telescope, CCD used, read-out noise, frame size, etc. the command LOAD/CCD can be used. This command reads these parameters for the MIDAS table eso_specs.tbl that, in case it is not present in your working directory, will be created. At initialization of the CCD context a copy of this table is put in the user's directory. In case non-ESO observing facilities have been used, or you want to modify or append the table with your own setup parameters, you can use the standard table commands e.g. EDIT/TABLE.