Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 749)

2.
Set the item.
Select [ Numbering ].
Select [ Continuous ] or [ Auto reset ].
If you want to reset the file numbering, select [ Manual reset ] ( ).
Select [ OK ] to create a new folder, and the file number will start with
0001.
Caution
If the file number in folder 999 reaches 9999, shooting will not be possible even if
the card still has free space. After a message requesting you to replace the card is
displayed, switch to a new card.
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