Canon MR-14EX II Manual De Instrucciones página 56

a: Advanced Multiple Flash Shooting with Slave A, B, and C Added
To fire flash tubes A and B and the slave unit at the same flash output, set
<_> and <j> in step 1. You can set any of A, B, or C
as the firing group for the slave units.
To add slave A and B only, set <%> and <l> in step 1.
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3
Take the picture.
Set the flash ratio for the firing group
(flash tube + slave) A:B and the flash
exposure compensation amount for
slave C, following the procedure
described in "Multiple Flash Shooting
with Slave C Added" (p.49), then take
the picture.