There, on a table at a neighborhood yard sale, you see an Acme Widget in its original box. You pick it up. On the box is the company address: Acme Widgets, Chicago 5, Illinois. How old is it?

Well, if you happened to know that the Zip Code was not introduced until July 1, 1963 (though not mandatory for bulk mailers until 1967), you would be able to tell from the postal area code (the number 5) that your new widget was over thirty years old. You can read all about it at the official USPS Web site, http://www.usps.gov/history/his1.htm#contents .

Later, at an estate sale, you find several porcelain knickknacks variously marked "Made in Occupied Japan," "Made in Nippon," "Japan," and "Made in Japan." How old are they?

If you had previously perused Kovels' New Dictionary of Marks http://www.amazon.com/exec/obidos/ASIN/0517559145/auctionbytescom , you would know that anything exported from Japan during the post-World War II Allied occupation (1945 to 1952) bore the "Made in Occupied Japan" mark.

And if you had visited AntiquesResources.com http://www.antiqueresources.com/articles/countrydating.html, you would have learned, among other things, that the McKinley Tariff Act of 1891 required that all imports be marked with the name of the country of origin, that the Act was revised in 1914 to require that "Made in..." be added. You would also have learned that Japan marked their wares "Made in Nippon" until 1921 when the law was changed again to require that names be in English. AntiqueResources.com has the best explanation of marks that I have found anywhere.

And how about patent dates? They're great for pinpointing the earliest date an item could have been produced. Found on everything from tools to jewelry, they identify the year the object was first protected. For lists of patent numbers and dates of issue, try the following sites:

The Official US Patent Office Web Site http://www.uspto.gov/web/offices/ac/ido/oeip/taf/issuyear.htm

Biddington's http://www.biddingtons.com/content/patentchart.html

Auntie Q's Antiques http://www.teleport.com/~auntyq/uspats.html (Auntie Q has also posted a list of British patent dates at http://www.teleport.com/~auntyq/britpats.html

Age is just one variable in determining the desirability of an item. But knowing the age is definitely helpful when you're considering purchasing an item to sell at auction.