Canon EOS-1D X Mark III Advanced User's Manual page 86

Vertical Shooting
Buttons, dial, and a Multi-controller for vertical shooting are arranged near the bottom of the
camera ( ).
When using the controls for vertical shooting, set the vertical-grip On/Off switch to
< >.
When you are not using these controls, set to <
operations.
Note
Vertical-grip Multi-function button 2 and the vertical-grip depth-of-field preview
button ( ) can also be used with the vertical-grip On/Off switch set to <
> to prevent unintended
86
>.