Canon SPEEDLITE 320EX Mode D'emploi page 38

Using Fully Automatic Wireless Flash
Flash exposure compensation and other settings set with the master
unit will also be automatically set in the slave unit(s). Thus, you need
not operate the slave unit(s). Wireless flash shooting with the following
settings can be done in the same way as with normal flash shooting.
• Flash exposure compensation
• FE lock
• Manual flash
With FE lock, if even one Speedlite results in underexposure, the <D> icon
will blink in the viewfinder. Open the aperture more or move the slave unit
closer to the subject.
Slave Group Control
Slave group A
Group = A Group = A
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For example, if you have the slave ID set
to <A> for three slave units, all three
slave units will be controlled as if they
were one Speedlite in slave group A.
Group = A