The E Button; Adjusting Exposure Compensation - Nikon D6 Reference Manual

The E Button

Use the E (exposure compensation) button to alter exposure
from the value suggested by the camera. Exposure
compensation can be used to make pictures brighter or darker.
−1 EV

Adjusting Exposure Compensation

Hold the E button and rotate the main command dial.
•
Higher values make the subject brighter, lower values darker.
•
Normal exposure can be restored by setting exposure
compensation to ±0.0. Exposure compensation is not reset
when the camera is turned off.
No exposure
compensation
+1 EV
The E Button 117