The INSTRUMENT extension contains instrument-specific information, which is defined separately for each instrument supported by ASTERIX. For details see the relevant instrument interface documents (e.g. USER_002 for EXOSAT).
One important component commonly present in the INSTRUMENT structure is SORT. This contains information about the ranges in the data dimensions (time, energy, x, y) over which data have been accumulated to form the binned dataset. These ranges are initially established in the event sorting, or are defined by the instrument itself (if it generates ready binned data). Some of the data dimensions may have disappeared in the binning process, so that preservation of the range information may be important for subsequent software, or for user information. The structure of SORT varies in detail from one instrument to another.