I can find plenty of catalogs that mention it, and the P2/F2 manual mentions it in passing, but I can't find a detailed breakdown of the back anywhere. I can basically figure out how it works, but there's an extra little metal lever on the top of the back to the right of where you'd put the metering probe in that doesn't look like anything I'm familiar with from my 4x5 back, and I can't for the life of me figure out what it's supposed to do