The value of _diffrn_detector_element.center is the Y
component of the distortion-corrected beam centre in
millimetres from the (0, 0) (lower-left) corner of the
detector element viewed from the sample side.
The X and Y axes are the laboratory coordinate system
coordinates defined in the AXIS category measured
when all positioning axes for the detector are at their zero
settings. If the resulting X or Y axis is then orthogonal to the
detector, the Z axis is used instead of the orthogonal axis.
Because of ambiguity about the setting used to determine this
centre, use of this data item is deprecated. The data item
which is referenced to the detector coordinate system and not
directly to the laboratory coordinate system should be used