Canon EOS-1 DX Mark III Advanced User's Manual page 856

C.Fn9
Clear all Custom Func. (C.Fn)
Selecting [ 9: Clear all Custom Func. (C.Fn)] clears all Custom Function settings.
Note
Customized operations for [ 6: Custom Controls], [ 7: switching ( /
)], and [ 7: Smart controller] are not cleared if you perform [ 9: Clear
all Custom Func. (C.Fn)]. Note that although information added using [ 8: Add
IPTC information] is retained, the setting changes to [Disable].
Settings for [ 3: AE Microadjustment] and [ 3: FE Microadjustment] are set
to [Disable] but not cleared when [ 9: Clear all Custom Func. (C.Fn)] is
performed.
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