Nikon D3300 - Manual (Page 268)

248 B The Setup Menu: Camera Setup
Choose On to use the exposure indicator to determine whether
the camera is correctly focused in manual focus mode (
0 83;
note that this function is not available in shooting mode M, when
the exposure indicator instead shows whether the subject is
correctly exposed).
Rangefinder
G button
➜ B setup menu
Indicator Description
Subject in focus.
Focus point is slightly in front of subject.
Focus point is well in front of subject.
Focus point is slightly behind subject.
Focus point is well behind subject.
Camera can not determine correct focus.
A Using the Electronic Rangefinder
The electronic rangefinder requires a lens with a maximum aperture of
f/5.6 or faster. The desired results may not be achieved in situations in
which the camera would be unable to focus using autofocus (
0 76).
The electronic rangefinder is not available during live view.