*** For details on how to be removed from this list visit the *** *** CCP4 home page http://www.ccp4.ac.uk ***
One version of the history of the 2 sigma(I) limit: Lyle Jensen told me that when they converted from integrated Weissenberg cameras to diffractometers, they wanted to carry over the concept of "less-thans" or "unobserveds" so they could compare their new structure determinations with their old ones. The background fog on the films matched with a 2 sigma(I) cutoff from the electronic counters. I'm not sure who all was involved in arriving at the magic 2 sigma number, but it seemed to be taken up by many investigators at the time (1960s?) Ron
