[BCMA] What is it?

[Moderated BCMA subscriber listserv]

Hi everyone!
A family friend is trying to identify the object in the attached image.
This is all the information he had:

Does anyone know what this was used for calculating? Both rings rotate
clockwise freely but lock in this position when rotated counterclockwise.
It seems to be a very specific type of calculator but the Google has not
been very helpful.

Might deal with weights with the references to 16 (= number of ounces in a
pound)

The image seems to be from around 1904 to 1908


Has anyone seen one of these before? It's from Ontario, around Thunder Bay.


Thanks if you can help!

Maureen
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