Canon EOS-1D X Mark III Advanced User's Manual page 204

Flash Function Settings
The information displayed on the screen, position of display, and available options vary
depending on the Speedlite model, its Custom Function settings, the flash mode, and other
factors. For details on the Speedlite's functions, refer to the Speedlite's Instruction Manual.
Sample display
(1) Flash mode
(2) Wireless functions/
Firing ratio control (RATIO)
(3) Flash zoom (flash coverage)
(4) Shutter synchronization
(5) Flash exposure compensation
(6) Flash exposure bracketing
Caution
Functions are limited when using EX series Speedlites that are not compatible with
flash function settings.
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