Canon EOS 1D Mark II Instruction Manual page 50

Instead of a white object, an 18% gray card (commercially available) can
produce a more accurate white balance.
50
4
Import the white balance data.
¡Hold down the <
5
turn the <
let go of the <
s
The image's white balance data will be
imported.
5
Select < O
¡Hold down the <
5
the < > dial to select <
go of the <
s
The custom white balance will be set.
X
> button and
> dial to select [OK]. Then
X
> button.
>.
B
> button and turn
O >. Then let
B
> button.