there already is a variable that the users can access to determine if
the file is DATA or GSIM....here's a piece of code...
IF (EVTYPE .EQ. -3) THEN
CVTYPE = 'ClasSim'
ELSEIF (EVTYPE .EQ. -2) THEN
CVTYPE = 'GEANT '
ELSEIF (EVTYPE .EQ. -1) THEN
CVTYPE = 'SDA '
ELSE
CVTYPE = 'DATA '
ENDIF
EVTYPE is held in the clasmdl.inc common block.....
hope this helps...
Arne