ISIS background subtraction

Hello, 

I have a few questions about the background subtraction in ISIS.

1. I think there is an error in the "backsub" function at
p33 of the manual. The equation of
s.err = sqrt (s.err * s.err + b.err * b.err); 
should be
s.err = sqrt (s.err * s.err + b.err * b.err * scale * scale); .


2. I tried the "define_bgd" function, and tried "get_iback",
but it didn't work well. Please let me know how to define
the background.

isis> load_data("imbh.pi");
*** invalid uncertainties replaced
Couldn't read DETNAM keyword
TG_M keyword not set
TG_PART keyword not set
TG_SRCID keyword not set
1
isis> define_bgd(1, "imbh_bgd.pi");
*** invalid uncertainties replaced
0
isis> back = get_iback(1);
Couldn't get background for dataset 1
S-Lang Error: Intrinsic Error: called from line 1, file: <stdin>
NULL

Thanks,
Hironori

==============================================================
Hironori MATSUMOTO
Center for Space Research
Massachusetts Institute of Technology
NE80-6045
77 Massachusetts Avenue
Cambridge, MA02139-4307, USA
TEL: USA(1)-(617)253-8008
FAX: USA(1)-(617)253-8084
e-mail : matumoto_at_email.domain.hidden==============================================================
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