The general class of goniometer or device used to support
and orient the specimen.
If the value of _diffrn_measurement.device 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.