I asked the Seiko museum for information and this was the answer:
"
Dear Mr. Xxxx,
It seems to be a #10 line, manufactured from 1931 to 1945.
There are just a few materials we have, we couldn’t find any more.
Thank you for your inquiry.
SEIKO MUSEUM"
I did some research and this watch probably belonged to a Japanese officer captured during the WWII but, obviously, I'm not sure.
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