Kim Bunker didn't mention this in his interesting sketch of piano
benches, but some benches made for player pianos ("pumpers") had
a hinged slat on the back edge, so that the tilting seat -- many
benches had liftable seats, as a place to store sheet music -- could
be tilted forward by raising the slat.  This gave the seat a forward
slope and offered the person pushing the pumper pedals a bit of
resistance countering the tendency of his body to move back from the
piano as he pedaled.

Matthew Caulfield
Irondequoit, New York