I agree that it might have been a tracking concept.  I've seen two
Aeolian products from Great Britain that had eight long slots
positioned either side of center on tracker bars, tubed together and
operating a pneumatic tracker.  I liked the idea insomuch as the
over-all condition of the roll's edges were not important to the
correct tracking of the roll, which was centered using the long narrow
slots to sense where the roll alignment is.

Tom Binnall
Seattle