Canon 600EX-RT Instruction Manual page 100

C: Setting Custom Functions
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C.Fn-09:
0: ON (Enabled)
When the flash coverage is set to "Automatic <L>", it is automatically
adjusted to match the image sensor size of the EOS digital camera being
used. When mounted on a supported camera, <S> is displayed on the
LCD panel.
1: OFF (Disabled)
The flash coverage is not automatically adjusted to match the image
sensor size.
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C.Fn-10:
You can change the time until the slave unit's auto power off takes effect.
Note that when the slave unit's auto power off takes effect, </> is
displayed on the LCD panel. Set this function on each slave unit.
0: 60min (60 minutes)
1: 10min (10 minutes)
0
C.Fn-11:
When you press the test flash button of master unit, you can turn on the
power of slave units in the auto power off status. You can change the time
within which slave units in the auto power off status accept this function.
0: 8h (Within 8 hours)
1: 1h (Within 1 hour)
98
(Auto zoom for sensor size)
(Slave auto power off timer)
(Slave auto power off cancel)