Canon EOS-1D X Instruction Manual page 128

Setting the Image-Recording Quality
One-touch Image Quality Setting
Custom Controls let you assign image-recording quality to the <B>
button, Multi-function button 2, or depth-of-field preview button with
[One-touch image quality setting], so that you can temporarily switch
image quality settings at the touch of a button before shooting.
For details, see Custom Controls (p.343).
If [51: Record func+card/folder sel.] is set to [Rec. separately], you
cannot switch to the One-touch image quality setting.
Maximum Burst During Continuous Shooting
The number of shots for the maximum burst is displayed
on the right in the viewfinder. If the maximum burst for
continuous shooting is 99 or higher, "99" will be displayed.
The maximum burst is displayed even when a card is not inserted in the
camera. Make sure that a card is inserted before taking a picture.
If the viewfinder displays "99" for the maximum burst, it means the
maximum burst is 99 or higher. If the maximum burst decreases to 98 or
lower and the internal buffer memory becomes full, "buSY" will be
displayed in the viewfinder and on the top LCD panel. Shooting will then
be disabled temporarily. If you stop continuous shooting, the maximum
burst will increase. After all the captured images are written to the card,
the maximum burst will be as listed on page 126.
The maximum burst indicator in the viewfinder will not change even
when you use a UDMA CF card. However, the maximum burst shown in
parentheses on page 126 will apply.
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