Part of the earliest calendar watches produced by Bulova. This appears to be the first square dial/case design we have seen.
Fully working movement and date function after a full service and restoration. Last photo shows condition when purchased. Rusted hands, setting lever and cannon pinion.
Suggesting 1932 based on the 10AC movement date stamp which is also stamped with an open diamond as shown in the comments. This open diamond stamp appears on both examples of the 10AC movement that I have.
The calendar watches we have seen thus far all seem to be housed in various case models, suggesting that Bulova varied the production of these, possibly to gauge interest in a particular design and style.
I know of only five examples that exist.