Robbie asked yesterday, regarding 20er rolls:
If 70mm per second is the "exception," then, pray tell, what is
the well-defined speed of the "rule"?
See the scale definition at - ahem -
There is of course a more qualified answer, as each organ manufacturer
has his own idea about this. But with hand-cranked organs and rolls
without "spiral correction," it is obviously moot to discuss speed
differences of one or two millimeters per second.