The value of _diffrn_measurement.id must uniquely identify
the set of mechanical characteristics of the device used to
orient and/or position the sample used during the collection
of each diffraction data set.
If the value of _diffrn_measurement.id is not given, it is
implicitly equal to the value of
Either _diffrn_measurement.device or
_diffrn_measurement.id may be used to link to other
categories. If the experimental setup admits multiple
devices, then _diffrn_measurement.id is used to provide
a unique link.