A value that should be taken as a potential target value for the
               torsion angle associated with the specified atoms, expressed as
               the distance between the atoms specified by
               _chem_link_tor.atom_id_1 and _chem_link_tor.atom_id_4 in the
               referenced record in the CHEM_LINK_TOR list. Note that the
               torsion angle cannot be fully specified by a distance (for
               instance, a torsion angle of -60 degree will yield the same
               distance as a 60 degree angle). However, the distance
               specification can be useful for refinement in situations in
               which the angle is already close to the desired value.