The R Button; Viewfinder Photography - Nikon D6 Reference Manual

The R Button

Use the R button to view shooting
information or choose the indicators
displayed.

Viewfinder Photography

During viewfinder photography, you can
press the R button to view an
information display in the monitor. The
display lists such data as shutter speed,
aperture, number of exposures
remaining, and AF-area mode.
94 The R Button