Data items in the DIFFRN_STANDARD_REFLN category record details
               about the reflections treated as standards during the measurement
               of a set of diffraction intensities.
               Note that these are the individual standard reflections, not the
               results of the analysis of the standard reflections.
 
    loop_
    _diffrn_standard_refln.diffrn_id
    _diffrn_standard_refln.code
    _diffrn_standard_refln.index_h
    _diffrn_standard_refln.index_k
    _diffrn_standard_refln.index_l
     s1 1  3  2  4
     s1 1  1  9  1
     s1 1  3  0 10