Hi this is my Grandads watch which I would like to know a bit about , I'm not even sure which decade it is from , I know the strap is wrong , but should it have a leather strap and what colour for this style watch . Thanks in advance.

 

https://omegaforums.net/threads/vintage-omega-posting-guide.383/ You did pretty well on 2-4 but number one is where we need help. Most of the information about the watch is on the inside.