C+
C NAME:
C	smei_frm_ratio
C PURPOSE:
C	Set dark current ratio for camera 3, mode 1
C CALLING SEQUENCE:
	function smei_frm_ratio(tt)
C INPUTS:
C	tt	integer(2)	SMEI frame time
C CALLS:
C	Time2YMD, Time2Delta, Time2Day, Time2DHMS, Say
C	cTime2Str, cFlt2Str
C PROCEDURE:
C	The dark ratio is from a fit to a function
C	f(t) = 1-exp(-(t-b)/a)
C	where t is the number of days since 2003/04/15 0 UT
C	The fit is done by the IDL procedure smei_frm_darkratio.pro
C RESTRICTIONS:
C	The origin t0 (currently 2003/04/15 0 UT) MUST match the
C	origin in the IDL procedure!!.
C MODIFICATION HISTORY:
C	NOV-2005, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
C-
	    integer	tt(2)

	character	cSay*9		/'frm_ratio'/

	character	cTime2Str*80
	character	cFlt2Str *14
	integer		Time2Str

	integer		t0(4)		/2003,04,15,0/

	real		a		/ 496.586/
	real		b		/-300.222/

	integer		uu(2)
	integer		hms(4)

	call Time2YMD  (1,uu,t0(1),t0(2),t0(3))	! Time Origin
	call Time2Delta(tt,uu,uu)		! Difference with time origin
	call Time2Day  (0,uu,dd)		! Difference in days

	smei_frm_ratio = 1.0-exp((b-dd)/a)

	call Time2DHMS(tt,hms)			! At the beginning of each hour

	if (hms(2)*60+hms(3) .lt. 4) call Say(cSay,'I',cTime2Str('SMEI',tt),
     &	     'dark ratio is '//cFlt2Str(smei_frm_ratio,5))

	return
	end