Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 132)

3 Customizing AF Functions
132
You can set the method for changing the AF area selection mode.
9 M-Fn button
After you press the < S > button,
pressing the < B > button changes
the AF area selection mode.
9 Main Dial
After you press the < S > button,
turning the < 6 > dial changes the
AF area selection mode.
You can set the AF point or the AF area selection mode + AF point
separately for vertical shooting and horizontal shooting.
: Same for both vert/horiz
The same AF area selection mode
and manually-selected AF point (or
zone) are used for both vertical
shooting and horizontal shooting.
AF area selection method
Orientation linked AF point
When [ S 9 Main Dial ] is set, use the < 9 > to move the AF point
horizontally.