Launched in 1966, replaced by the date at 9 version during 1967, these are pretty rare. We have seen a fair few on here over the years; Arno sold several during the auction; and my very own collection started with one in silver :)

Personally, I prefer these to the later version - the dial is more balanced and the chrono seconds needle doesn't really get in the way of reading the date in practice, it's very fine.