The market value of your watches is constantly changing. There are three factors that will determine the value of an old watch: They are:
1) How desirable the watch is.
2) The condition the watch is in
3) How much someone is actually willing to pay for it.
A Book is available at your local Barnes and Noble, or Amazon.com. It is called "The Complete Price Guide to Watches", by Cooksley Shugart, Tom Engle, and Richard Gilbert. It is very popular book among collectors and will help you determine an estimate of what your watch is worth. Again, the true "value" of a watch is what someone is willing to pay you for it. Books can only give an idea of the value.
Another excellent way to find the value of your watch is to go to eBay. Search Completed auctions for watches similar to your own watch. Only watches that actually SOLD count... Too many people see a "buy-it-now" price, or an opening bid price, and immediately believe that is what their own watch is worth... Wrong!!! You should ONLY consider watches that actually sold to figure out the value. You can get a very, very good idea of the current market value if you find a watch that is similar to yours.
You could also pay to have it appraised. See section "WATCH REPAIR SHOPS" for helpful advice in finding a good watchmaker in your area to help you.