Hi Bindu, There are lots of descriptions of these concepts on the exafs.org web page. Check out the Tutorials page. I wrote about them in my book chapter on page 58. If you like, I can send you a copy. It is kinda big so you will need to have 8Meg space in your mail box. Shelly -----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov on behalf of Bindu R. Sent: Fri 1/9/2009 7:12 AM To: ifeffit@millenia.cars.aps.anl.gov Subject: [Ifeffit] Query regarding error bars Hi all, Could any tell me in a simple language about the error bars returned by the EXAFS fitting program? what do they exactly represent?How is it determined?How is the number of iterations decided.In addition to R-factor what are the other parameters which determines a good fit.For a R-factor ~0.001, if the value of chi2~10,000 and reduced chi2 ~ 500, can one consider the fit to be good even if one gets a good match to the experimental spectra. Bindu Dr.Bindu R. Visiting Fellow BG-37 DCMP&MS Tata Institute of Fundamental Research Homi Bhabha Road Colaba Mumbai-400 005 India Contact Number Lab- 022-2278 2256, 022-2278 2671 Mobile-919892536830 Add more friends to your messenger and enjoy! Go to http://messenger.yahoo.com/invite/