Google Books has a good indexing that indicates that it is indeed a different volume number for each successive year:
https://books.google.com/books?q=editions:0AFLRE72TppycJMndttvYZq8tME6x3...
There are two metal rods, each with a spring at the base, in holes in the front rail, or stretcher, of the seat frame. In the UP position, they fit into holes in the underneath of the seat frame at the front two corners. There are four holes on each side, so there are only four positions for the chair to recline.
There's another part that connects the rod to the cylinders at each end; it is set into a slot in the backside of the stretcher. When you turn the lever end of the rod, it depresses the cylinders and you can slide the chair back and forth to whichever of the four position you want.
The back doesn't lean back so much as the seat slides forward or backward and then the back of the chair goes with it because they're connected with a piano hinge. The back of the chair pivots on bolts at the rear ends of the armrests.
I didn't get it either until I took it apart. I'm also not positive how well it works when you are sitting in the chair. Maybe you have to adjust it before you sit down? I don't know.
There are hard rubber bumpers on the front stretcher where the seat frame slides back and forth over it. I thought this was a nice touch.
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