[ I asked Jan about the term "tracker organ" and it's relation
 [ to the "tracker bar" of the player piano, etc.   -- Robbie

The term tracker is translated into abstract (Dutch), Abstrakt (German)
and la vergette (French).

A tracker is a wooden lath, on one side connected to a key,  and
on the other connected with the wind-chest (D: windlade, G: Windlade,
F: le sommier) through the roller-board (D: welbord, G: Wellenbrett,
F: le abrege).

So, in a traditional organ one will find trackers, but no tracker-bar.

In the pianola however the tracker-bar is a mechanism, which ensures that
the paper roll keeps its track, by using tracker-arms or trackers to
correct things.

The same term is used for mechanical organs when using a paper roll.
And that's why the mechanism, where the cardboard passes through on
book-operated organs, (maybe not quite correctly) sometimes also is
called a tracker bar.

Jan Kilstra

 [ The English cognate "abstract" seems to be taken from the verb "to
 [ abstract" (or "to extract") meaning "to pull".  So the abstract organ
 [ has small sticks of wood which pull, to open (or "abstract") the
 [ valves.  The tracker-mechanism in the player piano assures proper
 [ tracking, and I guess that the tracker-bar "reads" or "tracks" the
 [ data holes, in the same fashion as the hunter "tracks" his prey!
 [ -- Robbie