The value below which the density measured using standard
chemical and physical methods lies. The units are megagrams
per cubic metre (grams per cubic centimetre).
_exptl_crystal.density_meas_gt and _exptl_crystal.density_meas_lt
should not be used to report new experimental work, for which
_exptl_crystal.density_meas should be used. These items are
intended for use in reporting information in existing databases
and archives which would be misleading if reported under