Nikon Z9 Mirrorless Camera - Manual (Page 614)

614 A Custom Settings: Fine-Tuning Camera Settings
When [ Center-weighted metering ] is selected, the camera assigns the
greatest weight to an area in the center of the shooting display when
setting exposure.
b5: Center-Weighted Area
G button
U A Custom Settings menu
Option Description
R [ Small ]
The camera assigns the greatest weight to an
area equivalent to a circle 8 mm in diameter.
S [ Standard ]
The camera assigns the greatest weight to an
area equivalent to a circle 12 mm in diameter.
T [ Average ]
Weighting is based on the average of the entire
frame.