I've just been assured by a Welte connoisseur that the holes into
the horizontal grooves in Welte tracker bars are not connected to any
suction source but open to atmosphere, so my previous suppositions are
out the window.

The inference must be that the grooves were intended to reduce suction
drag on the tracker bar.  But it's hard to see how this might work.

The drag on the roll is chiefly caused by the paper being sucked down
and deformed minutely into each tracker note hole and having to rise
out over its trailing edge.

There may be some airflow between the paper and the tracker bar towards
its note holes owing to the surface roughness of the paper (relative to
air molecule size), and thus suction and drag, but this must surely be
extremely small even aggregated over the length of the bar.  Perhaps
someone can peel a roll carefully away from a bar towards the note
holes and tell us how extensive and appreciable any such suction is.

And what does such possible airflow between the grooves and the note
holes, and over the tiny septum between adjacent note holes when one is
open, one closed, mean for bleed/valve behaviour?

Can atmospheric grooves be an idea without foundation that looked
good?

Patrick Handscombe
Wivenhoe, Essex, UK