The increment for each step for the specified axis
in degrees. In general, this will agree with
_diffrn_scan_frame_axis.angle_increment . The
sum of the values of _diffrn_scan_frame_axis.angle and
_diffrn_scan_frame_axis.angle_increment is the
angular setting of the axis at the end of the integration
time for a given frame. If the individual frame values
vary, then the value of
_diffrn_scan_axis.angle_increment will be
representative
of the ensemble of values of
_diffrn_scan_frame_axis.angle_increment (e.g.
the mean).