Canon EOS-1D X Mark III Advanced User's Manual page 914

Group J
The 9 AF points shown here are available for autofocusing. As the AF area selection mode,
choose from Spot AF, 1-point AF, or Expand AF area:
: Cross-type AF point. Offers excellent subject tracking and high-precision focusing.
: AF points sensitive to horizontal lines (AF points to the left and right of the center) or
vertical lines (AF points above and below the center). Manual selection is not available.
Enabled only when Expand AF area: manual selection is selected.
: Disabled AF points (not displayed).
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