Setting Master/Slave on the Canon 580EXII

I always forget how to do this so I'm blogging about it so I know right where to look and so maybe it helps one other person. 1. Press and hold zoom for about 3 seconds to get into the master/slave mode. 2. Rotate the wheel to select between "off", "master on" or "slave on". 3. Press the set button. Don't forget the set button. Happy multiple flash photography!