Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 397)

3.
Check and change the lens information.
(1) Registered number
Displaying lens information
Press the < > button.
The lens name is displayed with a 10-digit serial number. When the
serial number is displayed, select [
OK ] and go to step 4.
“0000000000” is displayed if the lens serial number is not recognized,
and in this case, enter the number manually.
For details on the asterisk “*” preceding some lens numbers, see Lens
Serial Number .
Entering serial numbers
Select the digit to be entered, then press < > so < > is displayed.
Enter the number, then press < >.
After entering all the digits, select [ OK ].
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