Old Germanic sterling ring sizer

Had this ring sizer for donkeys years and always wondered how old it was.
Some details
weight 40gms
main ring 6cm Diameter
readable text
"M.Zwatschka" "Wien" "J.PachXXXX" "Donath"(owners name?)
"875"(very faint on rear) "S"(possibly sterling under solder joint)
scale "1-20"
The rings look like they were hammered round which makes me think it might be reasonably old although I don't know when the ring numbering system came into being, That will set a limit on how old it could possibly be.
Any ideas??
Cheers
Stephen

 

It has America ring size numbers,maybe the company that made them was a German named company in the U.S.

 

Vienna is not in the US or Germany

 

That's a cool piece. Seems like it has some genuine age to it. Very nice.

 

Here's a jeweler named "Donath" who died in Vienna in 1922. (But even I think that's a bit of a long shot.

https://www.geni.com/people/Norbert-Donath/6000000015374815655

Debora