Apparently having an unbreakable mainspring was an important feature to advertise in that era, judging from this and other watch ads in that issue.
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If you want to geek out on vintage watch ads, check out this issue of Europa Star from 1964. It has a great article on the Bulova Accutron.
https://www.europastar.com/demo/EUROPASTAR_EUROPE_026_1964_002_0001/index.html#p=1
That was a nice find of the article on the Bulova Accutron the only vintage that I really like.👍