Nikon D6 Reference Manual page 881

d8: Limit Selectable Image Area
Choose the options that can be accessed by rotating a
command dial while pressing a control to which [Choose
image area] has been assigned using Custom Setting f3
[Custom controls].
Highlight an option and press 2 to
•
select; selected items are marked with a
check ( M ). To deselect (remove the
check from: U ) a selected option,
highlight it and press 2 again. Image
area options marked with a check ( M )
are available for selection via a command dial.
• Press J to save changes when settings are complete.
G button U A Custom Settings menu
A Custom Settings: Fine-Tuning Camera Settings 829