Do you have a vintage Leica lens or camera and are interested in finding out its age?
This French site allows you to enter the serial number of your item and it will provide you with the date it was manufactured.
I’ve found it useful over the years.
—Peter.
Prosophos 
I have a lens that says Leitz Wetzlar 2092758 Summicron 1:2/50 around the lens, .with lens cover What do I have, will it work on other cameras, does it have value, I really don’t need it. What can you tell me about it please.
My friend has a 1936 Leica camera with cover . May I know the value ? thanks