Dating a Gruen watch using only the serial number is impossible. Collectors of Gruen watches can only approximate the year of manufacture of their watches using the serial number. Because there are no accurate records that mark which Gruen serial numbers correspond to which years, Gruen watches are very difficult to date. Some Gruen wristwatches manufactured between 1935 and 1956 can be dated using their style number.
Gruen's method of serializing the movement of its watches was complicated, and the records have been lost or destroyed. Researchers have compiled serial number information using old advertisements and watch material catalogues, which can show what year certain types of watches began to be manufactured.
Some Gruen watches can be dated using their style number. The style number is found only on certain Gruen watches, so this method does not work for all watches. The style number is found stamped on the inside back of the watch case and is paired with the caliper number. Both are three-digit numbers, and they come in one of two formats: CCC-SSS or SSS/CCC. Once you have found the style number, you can use the online tool at Gruenwristwatches.com to discover what year or years that style was manufactured. The database only contains information for watches produced between 1935 and 1956