Nikon D90 User Manual page 326

The Command Dials
Choose a metering
*
method
It·~
3D color
matrix II
[}D
Center-
weighted
8
Spot
28
Recommended in most situations; selected
automatically in auto and scene modes.
Camera meters entire frame but assigns
greatest weight to center area (defaults to
8-mm circle in center of frame).
Camera meters circle 3.5mm (O.14in.) in
diameter (approximately 2.5% of frame).