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