Nikon D3300 Reference Manual page 150

3
Select Measure.
Highlight Measure and
press 2.
4
Select Yes.
The menu shown at right
will be displayed; highlight
Yes and press J.
The camera will enter preset
measurement mode.
When the camera is ready to measure
white balance, a flashing D (L) will
appear in the viewfinder and
information display.
130 P, S, A, and M Modes