Power of a 580 as a Master

Ok so I have a 580exII on camera for fill as a master, and another as a slave. I know how to set the slave power, but don't know how much power the master is putting out.

I am sure I am missing something really basic, but couldn't find it in the manual.

Any info would be much appreaciated

Thanks, Dave

If your flash is on wireless E-TTL, you can set the A:B ratios on the master. So if you've set 1:4 as your ratio, your master will be set at 1/4th the power of the slave (note, this is not 1/4 power, but one-fourth of whatever the metered light output of your slave is going to be)

If you're shooting on manual wirelessly, then you can set the power output of your master and slave right on the master unit. Just keep the slave on E-TTL and the master will handle everything.

Other than that.... well, rtfm