ALLOWED FORMATS

A summary of the changes which have been made to this format are listed in Table 2, along with the version of XSPEC with which they are compatible.

Table 1: Log of changes to the OGIP format for a single PHA dataset

HDUVERS	Date	XSPEC	Comments
		version
1.0.0	1992 July	$>$8.0	Original Arnaud etal format
1.1.0	1993 Sept	$>$8.0	Small changes to optional keywords
1.2.0	2001 Mar	$>$11.1	Allowed 4-byte integer CHANNEL number
			and AREASCAL and BACKSCAL as vectors
1.2.1	2004 Apr	All	Allowed 2-byte COUNTS