Nikon D3X User Manual page 361

A
Virtual Horizon
When [Virtual horizon] is selected for [FUNC. button press], the electronic
analog exposure displays in the viewfinder and top control panel act as a
horizontal level when the Fn button is pressed.
Camera tilted right Camera level Camera tilted left
Control panel
Viewfinder
Note that the display may not be accurate when the camera is tilted at a
sharp angle forward or back.
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