Canon EOS-1D X Mark III Advanced User's Manual page 233

Note
During AEB shooting, the < > icon in the viewfinder and the < > icon on the
top LCD panel blink.
If the drive mode is set to < / >, press the shutter button three times for each
shot.
In < / / / / > modes, holding down the shutter button
completely captures three images, one after another, before the camera
automatically stops shooting. When < or > is set, three consecutive shots
are captured after a delay of approx. 10 or 2 sec.
You can set AEB in combination with exposure compensation.
Ends of the exposure level indicator are displayed as < / > or < / > when
the AEB range exceeds ±3 stops.
AEB is not available in flash photography or bulb exposures.
AEB will be canceled automatically if you do any of the following: Setting the power
switch to < > or when the flash is fully charged.
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