Dear friends of mechanical music, in response to Jim Miller's
questions about the Popper "Stella" (in 210531 MMDigest) I can give a
hint to Hans-W. Schmitz's recent article about the cooperation between
Popper & Co., Leipzig, and M. Welte & Söhne, Freiburg, which can be
easily accessed through the following link at our Society's website:
https://www.musica-mechanica.de/media/PDF/Kooperation_Popper_Welte.pdf 
The true scale of Popper's Stella is described on pp. 20-21 of that article.

Also, you'll find a discussion on the differences and similarities of
Welte and Popper music rolls. The article can be downloaded. Since it is
PDF/A you possibly may mark the text and let it translate to English,
e.g. with DeepL at https://www.deepl.com/translator 

The results are quite good with that translator and 200% better than
Google's translator which produces lots of errata and misunderstandings.
The DeepL translator may be used for free.

Regards,

Uwe Gernert - Editor "Das mechanische Musikinstrument"
Gesellschaft fuer Selbstspielende Musikinstrumente
Germany