Per Julian Dyer's excellent write up on the factors that affect Tempo
indicator calibration [120327 MMDigest]:  One of the other factors
affecting a pianolist's expression capability is how the rolls were
marked in the first place.  While I give Aeolian top grades in marking
versus the other brands, they were far from perfect if one listens to
a professional playing the same piece.

I am sure there was much effort in coming up with all those marks, but
two things still stuck in the way of perfection:  (1) How accurate the
printer timing was to the musical score and how far ahead of the music
was the marking?  (2) Were these actual representations of intended
expression versus someone's preference?

I say the actual gauge of correctness is the listener's ear despite how
accurately your Tempo gauge is calibrated.  Tempo changes within the
roll are all relative to the original Tempo and the how accurate the
stepping rate of the perforating punch was.

Just my $.02.

Ragards,
Dave Haibach