[ Ref. Matthew Caulfield in 200204 MMDigest -- ]
 [ http://www.mmdigest.com/Attachments/20/02/04/200204_161221_unnamed.jpg
 ]

Whatever was mounted on top of that mechanism would stay level as it
was rocked forward and back.  The spring pressure apparently can be
adjusted.  Seems like a ride to me.

Robert Bartlett