British Moses Thomas Pocket Watch

I'm trying to decipher the symbols inside this Moses Thomas key wind watch, and any help would be appreciated. I've translated the lion and anchor (silver and the Birmingham Assay Office, respectively), but the "m" date code and the "JR" in the diamond have me stumped.

Also, can anyone give me some guidelines as to how much more valuable the watch would be if it were running (sadly, it is not working now)?