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Item _phasing_MIR_der.R_cullis_anomalous

Description

              Residual factor R~cullis,ano~ for anomalous reflections for this
               derivative.

               The Cullis R factor was originally defined only for centric
               reflections.  It is, however, also a useful statistical
               measure for anomalous  reflections, which is how it is used in
               this data item.

               This is tabulated for acentric terms.  A value less than 1.0
               means there is some contribution to the phasing from the
               anomalous data.

                            sum |Fph+~obs~Fph-~obs~ - Fh+~calc~ - Fh-~calc~|
            R~cullis,ano~ = ------------------------------------------------
                                   sum|Fph+~obs~ - Fph-~obs~|

               Fph+~obs~  = the observed positive Friedel structure-factor
                            amplitude for the derivative
               Fph-~obs~  = the observed negative Friedel structure-factor
                            amplitude for the derivative

               Fh+~calc~  = the calculated positive Friedel structure-factor
                            amplitude from the heavy-atom model
               Fh-~calc~  = the calculated negative Friedel structure-factor
                            amplitude from the heavy-atom model

               sum is taken over the specified reflections

               Ref: Cullis, A. F., Muirhead, H., Perutz, M. F., Rossmann, M. G.
                    & North, A. C. T. (1961). Proc. R. Soc.  London Ser. A,
                    265, 15-38.

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