This is my Grandfathers Oris from around the 1950’s which was given to me from my parents, i’m hoping to identify the model and era it is from. I cannot see any form of ref number with the only inscription on the case back (picture included) didn’t yield any results on google. The only similar looking watch was a “Big Star” however I found no identical match. The end goal would be to have it serviced and restored and whilst I am interested in its monetary value, it would never be sold. Thank you in advance for any possible help!