SOPP434: Can you explain how crescendo roller works?

This question was sent by Alan. And he’s a member of the team who transcribes fingering and pedaling from the videos, and prepares nicely done fingering and pedaling practice scores. So Alan writes: Vidas and Ausra, I enjoyed this episode, thanks. You mention Sauer’s crescendo roller. We saw one of these demonstrated by Andreas Sieling when we toured the Berliner Dom last year. I didn’t quite understand this unique device ; perhaps you could explain exactly how it works in a future episode. Is it selectable to specific manuals? Does it change wind pressure or add/subtract from registrations? Thanks and regards, Alan Peterson