vintage oris star

My grandfather passed away a couple of months ago and we found this Oris Star among his belongings and I was wondering if anyone knew anything about this watch? It still works and appears to keep good time. The crown will not change the day / date (Coincidence that it is correct!) The back...

Greetings...my first post. Just like to show off a recent acquistion...a vintage Oris Star. I don't know much about it so if anyone can help fill in any details, please post. I bought my first Oris, a classic rectangular, almost 15 years ago...still a charmer and a lot less bling than some...