Jeff Davis asked, in 980805 MMDigest:

> Above the middle 16 tracker holes were pairs of long, thin
> vertically-oriented holes.  The owner said she found a date
> of 1914 for manufacture.  Does anyone know the use of these odd
> holes?  Perhaps suction could be applied in reroll, to act
> as a brake.

This was the Philipps tracking system, licensed from the German firm
who made the Ducanola plain player and Duca reproducing piano (of which
I've never seen a working example -- it had metal components which
corroded).

The system works, or is meant to work,  with really badly torn or
damp-swollen rolls.  It relies on there being enough going on in the
middle of the roll to sense where the note perforations are.  Notes
should just miss the pairs of slots but, if the roll gets off track,
a hole will open a slot to atmosphere and the tracking will correct.

In the pianos I've seen with working systems the tracking is performed
using non-spring-loaded double pneumatics so that the roll can go on
some way without notes in the central region, simply staying in the
position last sensed.

This made conversion to orthodox double-finger tracking especially easy
-- rebuilders long before the 1940s were doing this because the slots
were even worse than the Standard four-hole system for filling with
paper lint.  But quite a few restorers are reactivating the old system
nowadays and provided it's looked after, it works very well.

It appeared on quite a few different Aeolian models before they bought
into the Standard four-hole system.  We can only guess why -- a drunken
bulk purchase of slotted tracker bars over schnapps in Berlin ?   Or
the E. Munck works at Gotha had just bought a whole lot when Aeolian
took them over to make Stecks in 1909 ?

Dan Wilson, London