Question Sub 5130/0

[Jimmylsv]

have a 5130/0, serial number reflects 1977 year made. have worn everyday for 30 years. I’m in construction, diver and fish . I never take the watch off. it’s amazing the durability of the sub.

My questions, what does the /0 mean after 5130.
Also I was at a jewelry store to pick up chain for a gift. The jeweler that sells Rolex asked to look at watch. The bezel does not click like the new ones. Is it supposed to? It never has clicked, I’ve had watch serviced at Rolex , and I can turn either direction.
Any info would be great