The overall standard uncertainty (estimated standard deviation)
               of the displacement parameters based on the crystallographic
               R value, expressed in a formalism known as the dispersion
               precision indicator (DPI).

               The overall standard uncertainty (sigma~B~) gives an idea
               of the uncertainty in the B values of averagely defined
               atoms (atoms with B values equal to the average B value).

                                      N~a~
               (sigma~B~)^2^ = 0.65 ---------- (R~value~)^2^ (D~min~)^2^ C^-2/3^
                                    (N~o~-N~p~)


               N~a~     = number of atoms included in refinement
               N~o~     = number of observations
               N~p~     = number of parameters refined
               R~value~ = conventional crystallographic R value
               D~min~   = maximum resolution
               C        = completeness of data

               Ref: Cruickshank, D. W. J. (1999). Acta Cryst. D55, 583-601.

                    Murshudov, G. N. & Dodson,
                    E. J. (1997). Simplified error estimation a la
                    Cruickshank in macromolecular crystallography.
                    CCP4 Newsletter on Protein Crystallography, No. 33,
                    January 1997, pp. 31-39.

                   http://www.ccp4.ac.uk/newsletters/newsletter33/murshudov.html