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).