Temperature in kelvins below which _exptl_crystal.density_meas
               was determined. _exptl_crystal.density_meas_temp_gt and
               _exptl_crystal.density_meas_temp_lt should not be used for
               reporting new work,  for which the correct temperature of
               measurement should be given. These items are intended for
               use in reporting information stored in databases or archives
               which would be misleading if reported under
               _exptl_crystal.density_meas_temp.