John Tuttle was asking about a Gulbransen "fishing pole" tracking
system.  It may only be a lead, but many years ago I had a piano with
an H.C. Bay player action that used such a scheme.  It worked quite
well, using only very light physical contact to "feel" the two edges
of the paper.  I admired the clever design feature that automatically
accommodated the different paper widths used early-on.

Bill McKeown