The R factor for merging the reflections that satisfy the
          resolution limits established by _diffrn_reflns.d_resolution_high
          and _diffrn_reflns.d_resolution_low and the observation limit
          established by _diffrn_reflns.observed_criterion.
                           
               Rmerge(I) = [sumi(sumj|Ij - |)] / [sumi(sumj)]
                                
               Ij = the intensity of the jth observation of reflection i
                 = the mean of the amplitudes of all observations of
                      reflection i
               sumi is taken over all reflections
               sumj is taken over all observations of each reflection