Zenith cal 10.5, 18jewels, 30s?

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Hello.
I acquired this 10.5 cal Zenith. It probably dates from the 1930s. It appears to be in pretty good condition and is little piece!
I'd appreciate it if anyone could provide any information on the model/date/etc. (and any questions about authenticity?)

 
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I've seen a few watches like this, but none of them had a movement cal. 10.1/2 with a regulator.
Plus, 18 jewels is a lot for the 1930s.