A simpler way to sift through the serial-number-to-watch-reference tables, and you get an estimated production date as well as links to the Speedmaster101 website. @uwsearch illustrated a nice way to date Lemania's based on serial number. I have found this table very useful in looking at vintage Lemania's (especially issued ones, that may have dates stamped on them). @WurstEver later proposed a nice idea about using extracts to create a similar table as above, thus guessing the production date more accurately than Hartmann's table . For y'all : www.ilovemyspeedmaster.com This is a tool that implements a unique algorithm to give a slightly more accurate result than any methods suggested (or freely available on the internet). It deals with overlapping data much better than the simple methods provided...and as it gets more extracts, so the data gets more crazy, especially later on. I digress... Enter a movement number (321, 861 and 1861 Moonwatches only) and get a predicted production date based on the current available extracts (or enter a birthdate and get a range of SN's). You also get the matching entries in the MWO Tables (which came out a week after creating this thread ). And then it uses the reference(s) found to provide 'current market value' using the Speedmaster101 price chart, with a link to the excellent pages about the particular watch. You can anonymously upload archive extracts too : please help make this tool as good as possible for all your fellow horologists. Thanks to Greg for giving his permission to use the MWO tables. Thanks to William for giving his permission to use the Speedmaster101 price tables. Thanks to all the members who have uploaded their extracts.