The increment after this frame for the angular setting of
              the specified axis in degrees.  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 and should equal
              _diffrn_scan_frame_axis.angle  for this next frame.