John Tuttle's unusual tracker bar includes a short-lived tracking
system.  The extra slots are positioned in pairs above the central
tracker bar note holes and are connected to two outputs, all right hand
together and all left hand together.  These are then used in place of
margin tracking holes at the extreme ends of the tracker bar.
The basis of this arrangement is that there will always be note holes
going past the tracker bar in this centre section so there will always
be a tracking correction output.  This system is not affected by worn or
torn roll edges, neither is it affected by the notes being punched
slightly off line since the notes themselves are tracked rather than the
paper.  Clever eh?

This design was obviously not a success as it is rarely seen, and on
John's example has been replaced by the more conventional early double
mechanical ear system.  Either that or the piano was never fitted with
the system and an obsolete tracker bar was used to use up old stock.
Are there any MMDers out there who have a piano fitted with this system
and have it working?

Kind regards from Great Britain,  Nicholas Simons.