I am not sure what all the markings on the case mean and some I can’t read. I believe it’s the 6BK Movement. The markings inside the case that I could read are 17 jewels, SF, Fifth Avenue New York, Swiss. There is either BL39, BL37, 3437...I can’t tell. The band says Speidel pat 2689450
Welcome to myBulova and thank you for sharing your watch with us. It is a Margo with a lovely two tone model like this one https://mybulova.com/watches/1948-margo-9875. The markings on the inside of the case are service markings. It is a good sign that it was well taken care of to have so many service markings.
Bulova Margo
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