After all the work that should be done rebuilding the air motor,
governor, and linkages, I don't think anyone has mentioned that when
the pointer is set to 'Tempo 70' the roll will be playing at 70 or
some other figure.

To ascertain the actual Tempo, mark a music roll (not your good and
valuable roll!) at 5, 6 and 7 feet and every ten feet thereafter until
120 feet or so is reached.  Have a suitable time piece and record the
distance in the feet per minute (Tempo 70 is seven feet per minute,
etc.) corresponding to the figures marked on the roll.  Make a graph
if you like and it should be linear.  Adjustments to the pointer on
the scale can then be made.

I made a test of 250 feet of paper to know at what speed the "O" roll
is advancing at the various lengths, so as to determine the length of
the "time scale" (length of one musical measure bar) to be used for a
certain tune at a given number of feet that have 'gone by'.

A graph was made and I found it not linear in that from 50 to 100 feet
there was a curve, an increase, then it settled down and after the 100
feet mark it continued in a straight line.  This feature has nothing to
do with governors or roll motors as the paper is driven by an electric
motor.  I did check this test 3 more times on different days and still
got the same result.

Stephen Bentley - SB-"O" Rolls
Vancouver, British Columbia, Canada