Right. Getting the hang of it now. I set both flash heads up lastnight and connected them to the RB67. The lightmeter was positioned a couple of metres away while I fired the shutter. At first the meter reading was a bit odd but then this was because both flashes were aimed at it, once I started bouncing the slave flash from the ceiling I was able to control the power and get the readings I expected.

Helen, I don't know if I'll be using it much with the Canon as I've got the 550EX which is almost foolproof

My final question for now is using it for fill-flash. For example if I were to take a picture of a person with the main light (sun) from behind and get an incident reading of say, f8 would I then set the flash power to be something like f5.6 or f4?