How do thread/saddle stitching machines work?

Any good videos how they work? Or some manuals with insights?
Why are they so expensive?
Any help is very welcome, thank you very much in advance.
Best wishes,
Paul

 

Sorry I have no pictures presently. But briefly, thread saddle sewing works this way. Book section is opened and placed on saddle, saddle moves in towards needle side of the machine. Piercing needles move up underneath the book section and make holes for needle and hook. While piercing needle retreats, thread needle and hook descent from top and enter the pierced holes. Then thread carrier underneath moves and picks thread from needle and carries to hook. Hook picks thread and then needle and hook rise to their position. Cycle continues for next stitch. There may be more pairs of needles and hooks.