Bulova 1930 Rona
Case is 17mm X 26.75mm Lug end to lug end is 31mm Case has Bulova Qaulity on the inside and an "F" printed on outside case just under lug. Has a dust cover.
The closest picture I can see is for the 1930 "Rona" 18 of 36 top left of picture. Although my watch has a sapphire in the crown and the picture does not - may have had an older stem and crown fitted???
Don't know - will leave this up to you guys and gals.
Edit: 1927 advertisment shows "Rona" with the Sapphire in the crown.