A Window Washing Rig

This is 750 7th Avenue. Noticed this thing in use walking by the other morning. Because of the setbacks they use this interesting rig: an enormous arm that swings out to accomodate the setbacks, I assume. I also assume it's very scary getting to where hanging scaffolding is in this picture.

I know the building manager well so I'll ask him if he can't provide me with some juicy bits on the sequence of operation.