Hello, I need help with this Seikosha chronograph pocket watch. I bought it at a flea market recently and I'm looking for any information about it. I found the same watches as mine on the web but there is something that I cannot explain. Each of them has some writings and numbers on the back. Mine doesn't have it. But the rest including the case back inside looks completely the same, there are the same marks and that small writing SKS. What do you think about it? Can you tell me something more about it? Here are some pictures I made.