function abscal,value,header,DEBUG = debug
;+
; NAME:
;	ABSCAL
; PURPOSE:
;	Apply the FITS BZERO and BSCALE keyword values to a data array
;
; CALLING SEQUENCE:
;	RESULT = ABSCAL( Value, Header, /DEBUG)
;
; INPUTS:
;	VALUE -  Any scalar, vector, or array (usually an integer type giving a
;		relative intensity).
;	HEADER - A FITS  header array containing the absolute calibration
;		keyword BSCALE, and optionally BZERO and BUNIT.
;
; OUTPUT:
;	RESULT = BSCALE*VALUE + BZERO, where the BSCALE and BZERO scalars
;		are taken from the FITS header.  
;		If the absolute calibration keywords do not exist, then
;		RESULT = VALUE, and !ERR = -1.
;
; OPTIONAL INPUT KEYWORD:
;	DEBUG - If DEBUG is set, then ABSCAL will print the
;		calibration units given by the BUNIT keyword.
;
; REVISION HISTORY:
;	Written W. Landsman, STX Corporation     January 1987
;	Use DEBUG keyword instead of !DEBUG      September 1995
;-
  On_error,2
 
 if ( N_elements(value) EQ 0 ) then message, $
     'Array (first parameter) to be calibrated is not defined'   
 
 zparcheck, 'ABSCAL', header, 2, 7, 1, 'FITS Image header'
 bscale = sxpar( header, 'BSCALE')     
 if !ERR eq -1 then begin                 ;Did BSCALE keyword exist?
	print,'ABSCAL - No calibration keywords in FITS header'
	return,value
 endif

 bzero  = sxpar( header, 'BZERO')       ;Get BZERO keyword, 0 if not found
 if keyword_set(DEBUG) then begin                 ;Print calibration units          
    bunits = sxpar(header,'BUNIT')       ;Are calibration units supplied?
   if !ERR ne -1 then message,/INF,'Calibration Units: ' + bunits else $
	message,/INF,'Calibration Units not given'
 endif

 return,value*bscale + bzero        
 
 end