Nikon D4 User Manual page 185

The U Button
At settings other than K (Choose color temp.) and L (Preset
manual), the U button can be used to fine-tune white balance
on the amber (A)–blue (B) axis (0 157; to fine-tune white balance
when L is selected, use the shooting menu as described on
page 156). Six settings in both directions are available; each
increment is equivalent to about 5 mired (0 158). Press the U
button and rotate the sub-command dial until the desired value is
displayed in the rear control panel. Rotating the sub-command
dial to the left increases the amount of amber (A). Rotating the
sub-command dial to the right increases the amount of blue (B).
At settings other than 0, an asterisk ("U") appears in the rear
control panel.
Rear control panel
U button
Sub-command dial
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