[ccp4bb]: Contour

["Leslie A." <andrew@mrc-lmb.cam.ac.uk>]

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"Gerard \"DVD\" Kleywegt" writes:
 > i seriously disagree with your seriously disagreeing.
 > assume that the sigma level at the end of a refinement
 > is 0.0001 e/A3. then a 10-sigma feature is noise. my point
 > is that the "number of sigmas" of a feature in an fo-fc
 > map is meaningless - the absolute sigma level is not, of
 > course (but this assumes that you calculate your maps on
 > an absolute scale to begin with !).
 > 

I would suggest that your hypothetical example is not of any relevance
to macromecular crystallography. There are ALWAYS errors in a model,
even in the final stages of refinement, because there is never
sufficent data to be able to model all aspects of conformational
mobility/disorder. A 5 sigma peak in an Fo-Fc difference map, even
close to the "end" of refinement, can be interpreted with very high
confidence as indicating an error in the model. As I mentioned
earlier, in many cases it may not be possible to interpret these
features, but this does not mean they have no significance.

    Andrew Leslie