Case ref. 2887 for the constellation is the only screwback case reference that housed cal. 501/505 with the vast majority of connies with these movements being sold in snapback cases (maybe 99% from what I have observed). When Desmond wrote an article on this very uncommon case ref (http://omega-constellation-collecto.../omega-constellation-black-sheep-returns.html) almost 3 years ago I knew I had to get one someday but I wanted one in top notch condition. This one in my collection is a one owner watch - worn gingerly for about a year and then kept in a drawer for the next 50 years or so. It has its original leather strap (aged but intact and still wearable and even the spring bars are as they came from the factory) and buckle. And for the constellation fans, this example clarifies a couple of things about case ref. 2887 that were not previously recognized - the reference featured piepan dials as well as the earlier spelling of the word chronometRE. I hope you like the pictures.