              The code identifying a reflection measured as a standard\
               reflection with the indices _diffrn_standard_refln.index_h,\
               _diffrn_standard_refln.index_k and\
               _diffrn_standard_refln.index_l. This is the same code as the\
               _diffrn_refln.standard_code in the DIFFRN_REFLN list. 