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The default sigma cutoff (in denzo) is -3 and I wouldn't override that without good reason. The cut-off is applied before averaging equivalent reflections (but after adding partials?). If you reject all negative observations of a particular reflection and average the remaining positive observations, you will get an artificially inflated estimate of the intensity. Even if the intensity is negative after averaging, the French&Wilson treatment in truncate will give you a positive F in the end. Apparently there is some information in the negative reflections, i.e. the most likely value of Fobs for a reflection with Iobs= -0.01 sigma is greater than that for a reflection with Iobs=-1.5 sigma. Ed protein.chemist protein.chemist wrote: > What is the Sigma Cutoff that one should use for Data Processing using > HKL2000. > > Is there a minimum or maximum value. > > Also if there is a variation then what all does it depend on. > > Thanks in Advance for your help. > > Mariah > > -- > Mariah Jones > Department of Biochemistry > University of Florida