              The value of sigma~a~ used in constructing the Luzzati plot for\
               reflections classified as observed. The details of the\
               estimation of sigma~a~ can be specified in\
               _refine_analyze.Luzzati_sigma_a_obs_details.\
\
               Ref:  Luzzati, V. (1952). Acta Cryst. 5, 134-136.