Canon EOS-1DX MARK II Settings Manual page 28

In Case 5, [AF pt auto switching] is set to [+1]. This
means that in AF Area settings where the camera
automatically can change the active AF point —
Automatic AF point selection, Large Zone AF, and Zone
AF — the AF system will speed-up changing points to
follow a moving subject. As a result, even when the
subject continuously leaves the initial AF point, it is
possible to increase the ratio of photos that are in focus.
This setting is most effective when shooting distinctive
sports with subjects moving across the frame, such as
figure skating and skateboarding, or when the shooting
distance is close with relatively fast-moving subjects.
Unlike Case 6, Case 5 assumes the subject will be
moving at a relatively steady speed, even if it's changing
location in the frame from shot to shot.
A race motorcycle driving extremely close to the
photographer. With Case 5 selected, it is effective in
cases where it would be difficult to track a relatively fast-
moving subject with one point.
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