My Grandfather's Watch

This watch belonged to my grandfather who passed away 29 years ago at the age of 89. It seems to work properly but is clearly banged up a bit, probably because he carried it wherever he went, at work on the farm and at his stall at the St Lawrence Market in Toronto for many years. I would never sell it but I'm curious about its age, etc. If the back screws off to expose the serial number, I haven't been able to do that, since the glass front cover wants to unscrew instead.