Total of 27 possible channels, labeled 0..26, in order of ascending pitch.
Channel 13 lies on the center line of the paper.
Channels 1..20 comprise the standard "Carl Frei" or "Raffin" 20-note scale
employed by most 20-key organ builders. The use of the remaining channels
is not standardized.
paper width: 110 mm (4.33 inch)
hole diameter: 3 mm (0.118 inch)
channel spacing: 3.8 mm (0.15 inch)
number of channels: 20 typical, 27 possible
paper speed, typ.: 6 to 7 cm per second
