In Europe the hallmarking of precious metal objects was, and still is, a legally required process.
It involves testing and the fineness of the metal and then stamping it with control marks that show the results.
For many American watch brands, the age can be determined using the serial number from the movement (the "works") of the watch.
Many watch companies made hundreds of thousands of watches, and some companies made millions of watches!
It would be impractical to list the individual serial numbers of EVERY watch made... Our serial number tables list RANGES of serial numbers.
If you're buying or selling a car, it's not enough just to know that it's an old Ford.
You would need to know the year, model, engine size and type, whether it's an automatic or manual transmission, how many miles it has on it, what kind of condition it's in, what special features it had that made it more or less collectible, etc. In order to accurately determine value, you must first determine who made the watch (the manufacturer), and as much information as possible about the model, grade, age, size, quality and unique features of your watch.