C. R. Spillmann SA were case makers based in La Chaux de Fonds, they're famous for making the cases of the 1st Rolex oysters, as well as cases for many other watch manufacturers, such as UG, Zenith.
The particular Spillmann case design in the above UG example is a favourite amongst collectors and appears in many other contemporary chronographs from other makers, e.g. Doxa. Typically in steel though, would love to see other examples in solid gold from our various UG experts here!
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