As a post is worthless without pictures:


Very nice watch!
Sorry I don’t have more info for you.
But I do have a question:
The buckle (and maybe strap?) – is it original with the watch?
The thickness of the strap (thin) indicates old and the buckle shape is not a very often seen.
Possible the French reference was 10 R.S.C. 4.
French catalogue 1953:

And I guess the water-resistant version of your watch was the E 262.
French catalogue 1957:

Best
Blomman
I would say timeless and elegant.
Not specially rare, you will still have some issues to find one like yours in such a god condition.
The movement, the 478 is not specially rare, as 80 000 were made in 20 years ( 1945 - 1965 ).
But it is a good, reliable and accurate movement, which was used in another very interesting watch, the JLC SHOM. Here is a link which may be of some interest: