Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 165)

Note
In the viewfinder, maximum display of the number of shots available is 1999.
is set automatically if you set both RAW and JPEG/HEIF to [ ].
Two versions of each shot are recorded at your specified image quality when you
have selected both RAW and JPEG/HEIF. Both images have the same file number
but each has a different file extension, with .JPG for JPEG, .HIF for HEIF and .CR3
for RAW.
<
>/< > appears at the right in the viewfinder based on your JPEG/RAW
selection.
Meanings of image size icons are as follows:
: RAW, : Compact RAW,
JPEG: JPEG, HEIF: HEIF, : Large, : Medium 1, : Medium 2, : Small.
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