That strange looking tracker bar is from a piano that had the Solo
Carola inner player system.  It was a form of expression player piano
that attempted to control the travel of _each_ hammer and by doing
that, effect the strike power of hammer to string.

I would say it was like two player actions in one piano.  The one
action was the regular system to strike the notes and that was
connected to the square holes.  The expression device was another
complete set of pneumatics that had metal fingers and pads that would
push the hammer closer to the string.  This part was connected to the
long thin slots in the tracker bar.  The basic idea was to pre-set the
hammer travel before the note was called for.

I maybe still have a few rolls for this system on a shelf someplace.
I can only imagine that getting proper registration of the paper roll
would be quite a trick.  The note holes were punched out of the paper
in the normal size.  The control holes were very narrow slits.

Sorry, but I can't recall the make of piano I found this system in.
It was in Canada and it was foot pumped.

I guess there was no end to the imagination of developers of player
systems back in the day.

Best to all,
Ken Vinen, Aylmer, Ontario, Canada