Canon EOS-1D X Mark III Af Setting Manualbook page 55

When using the optical viewfinder, selection of the
zones can be made from up to nine focusing zones.
During shooting with the optical viewfinder, the AF points
are divided into three blocks, left, center, and right, and
each has upper, central, and lower zones, and the desired
location can be selected from these nine zones.
The position can be set more precisely on the subject during
Live View shooting.
Viewfinder shooting
Live View shooting
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