Canon EOS-1D X Mark III Advanced User's Manual page 399

4.
Make the adjustment.
Single focal length lens
Zoom lens
For a zoom lens, select the wide-angle (W) or telephoto (T) end.
Pressing <
Set the adjustment amount, then press <
±20 steps.
Setting it toward "–:
standard point of focus.
Setting it toward "+:
standard point of focus.
For a zoom lens, repeat this procedure and adjust it for the wide-angle
(W) and telephoto (T) ends.
After completing the adjustment, press the <
to the screen in step 1.
> clears the purple frame and enables adjustment.
" will shift the point of focus in front of the
" will shift the point of focus to behind the
399
>. The adjustment range is
> button to return