Nikon D6 Reference Manual page 915

Pitch
Camera tilted
forward
•
Note that the display may not be accurate when the camera is tilted at a
sharp angle forward or back. The camera will not display pitch and roll
indicators when held at angles at which tilt cannot be measured.
•
The roles of the pitch and roll indicators are reversed when the camera
is rotated to take pictures in "tall" (portrait) orientation.
f4: Multi Selector Center Button
Choose the role assigned to the center of the multi selector
during playback and still photography.
Camera level
G button U A Custom Settings menu
A Custom Settings: Fine-Tuning Camera Settings
Camera tilted back
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