Canon EOS-1D X Mark III Af Setting Manualbook page 121

You can also use C2 and C3 in the [ 3]
tab [Restrict shooting mode].
Check C2 and C3 and set
[OK]
There are three custom shooting modes, including [C2]
and [C3]. Only [C1] can be used by default, but by adding
ticks to [C2] and [C3] in [Restrict shooting modes], they
can also be used. When [Switch to Custom Shooting Mode]
is assigned to the
to switch from [C1] → [C2] →[C3] →. When only one setting
is frequently used, enabling only [C1] makes faster switching
possible.
C2 and C3 can also be
selected
〈 〉
button, press the
121 121
〈 〉
button