Canon EOS 7D Instruction Manual page 132

Using Wireless FlashN
Setting the Flash Output Manually for Wireless Flash
When [Flash mode] is set to [Manual flash], the flash output can be set
manually. The flash output settings ([1 flash output], [Group A
output], etc.) that can be set will differ depending on the [Wireless
func.] setting (see below).
132
[0]
The flash output set manually is

applied to all external Speedlites.
[0 (A,B,C)]
The flash output can be set manually

and individually for each group (A, B,
and C) of external Speedlites.
[0+3]
The flash output can be set manually

and individually for external Speedlite
and for the built-in flash.
[0 (A,B,C) 3]
The flash output can be set manually

and individually for each group (A, B,
and C) of external Speedlites and the
built-in flash.