A minimal number of keywords has been defined as part of the FITS standard,
but additional ones can be (and have been) added by various groups to
support their own needs. Thus, several ``flavors'' of FITS coexist. A
detailed description of the CLASS FITS flavors is given in
chapter . Unknown keywords are normally ignored, but
CLASS supports FITS keyword redefinition. If you receive a file with
scan number coded as NUMBER (instead of SCAN-NUM), all you need
to do is to define a SIC symbol named NUMBER with translation SCAN-NUM. This is done by typing SIC
SYMBOL NUMBER
SCAN-NUM.