Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 330)

Registering AF Points
You can register the position of a frequently used AF point. For instant switching from the
current AF point to your registered AF point, you can use a button you assign on advanced
setting screens for [
Metering and AF start ], [ Switch to registered AF point ], [ Direct AF
point selection ], or [ Register/recall shooting func ], in [ 6 : Custom Controls ] ( ).
For instructions on registering AF points, see Custom Controls .
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