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

/1/ channel number
/2/ note played by Jaeger & Brommer 20er Drehorgel, German music notation
/3/ MIDI note number
/4/ remarks

/1/	/2/	/3/	/4/

1	F	53F
2	B	58A#	(B-flat)
3	c	60C	"Middle C"
4	d	62D
5	ds	63D#	(E-flat)
6	e	64E
7	f	65F
8	g	67G
9	a	69A
10	b	70A#	(B-flat)
11	c'	72C
12	d'	74D
13	ds'	75D#
14	e'	76E
15	f'	77F
16	g'	79G
17	a'	81A
18	b'	82A#	(B-flat)
19	c''	84C
20	d''	86D

The image shows a portion of a 20er music roll, maker unknown, punched ca. 1998 for Jaeger & Brommer.  The handwriting is by Wolfgang Brommer; he rejected this roll because of its poor quality.

image file: 20er_c.jpg (43 kb, 150 dpi)