Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 188)

u White Balance Correction
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During white balance bracketing, the maximum burst for continuous
shooting will be lower.
Since three images are recorded for one shot, it takes longer to record
the image to the card.
You can also set white balance correction and AEB together with white
balance bracketing. If you set AEB in combination with white balance
bracketing, a total of nine images will be recorded for a single shot.
When white balance bracketing is set, the white balance icon will blink.
You can change the sequence (p.424) and number of shots (p.425) for
the white balance bracketing.
“ Bkt. ” stands for bracketing.