Thanks for the link, as it happens I have the original manual for the flash meter (yes, it came with the manual but without the dome, great huh!) but it makes no reference to the switch. I was hoping that someone else out there has a Flash Meter III and could visually check the operation of the switch. The other idea I had was to take it to a camera shop and see if they would let me compare meter readings with another flash meter so as I could see if the meter readings were the same, but figured I'd ask you guys first.

Cheers,
Philip